Academic Commons Search Resultshttp://academiccommons.columbia.edu/catalog.rss?f%5Bsubject_facet%5D%5B%5D=Hydrologic+sciences&q=&rows=500&sort=record_creation_date+desc
Academic Commons Search Resultsen-usGlobal and Regional Aspects of Tropical Cyclone Activity in the CMIP5 Modelshttp://academiccommons.columbia.edu/catalog/ac:187388
Camargo, Suzana J.http://dx.doi.org/10.7916/D81R6PQWThu, 23 Jul 2015 12:57:44 +0000Tropical cyclone (TC) activity is analyzed in 14 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). The global TC activity in the historical runs is compared with observations. The simulation of TC activity in the CMIP5 models is not as good as in higher-resolution simulations. The CMIP5 global TC frequency is much lower than observed, and there is significant deficiency in the geographical patterns of TC tracks and formation. Although all of the models underestimate the global frequency of TCs, the models present a wide range of global TC frequency. The models with the highest horizontal resolution have the highest level of global TC activity, though resolution is not the only factor that determines model TC activity. A cold SST bias could potentially contribute to the low number of TCs in the models. The models show no consensus regarding the difference of TC activity in two warming scenarios [representative concentration pathway 4.5 (RCP4.5) and RCP8.5] and the historical simulation. The author examined in more detail North Atlantic and eastern North Pacific TC activity in a subset of models and found no robust changes across models in TC frequency. Therefore, there is no robust signal across the CMIP5 models in global and regional TC changes in activity for future scenarios. The future changes in various large-scale environmental fields associated with TC activity were also examined globally: genesis potential index, potential intensity, vertical wind shear, and sea level pressure. The multimodel mean changes of these variables in the CMIP5 models are consistent with the changes obtained in the CMIP3 models.Atmospheric sciences, Hydrologic sciences, Geophysicssjc71Lamont-Doherty Earth ObservatoryArticlesInfluence of local and remote SST on North Atlantic tropical cyclone potential intensityhttp://academiccommons.columbia.edu/catalog/ac:187385
Camargo, Suzana J.; Ting, Mingfang; Kushnir, Yochananhttp://dx.doi.org/10.7916/D8988677Thu, 23 Jul 2015 12:39:46 +0000We examine the role of local and remote sea surface temperature (SST) on the tropical cyclone potential intensity in the North Atlantic using a suite of model simulations, while separating the impact of anthropogenic (external) forcing and the internal influence of Atlantic Multidecadal Variability. To enable the separation by SST region of influence we use an ensemble of global atmospheric climate model simulations forced with historical, 1856–2006 full global SSTs, and compare the results to two other simulations with historical SSTs confined to the tropical Atlantic and to the tropical Indian Ocean and Pacific. The effects of anthropogenic plus other external forcing and that of internal variability are separated by using a linear, “signal-to-noise” maximizing EOF analysis and by projecting the three model ensemble outputs onto the respective external forcing and internal variability time series. Consistent with previous results indicating a tampering influence of global tropical warming on the Atlantic hurricane potential intensity, our results show that non-local SST tends to reduce potential intensity associated with locally forced warming through changing the upper level atmospheric temperatures. Our results further indicate that the late twentieth Century increase in North Atlantic potential intensity, may not have been dominated by anthropogenic influence but rather by internal variability.Geophysics, Hydrologic sciences, Climate changesjc71, mt2204, yk16Lamont-Doherty Earth ObservatoryArticlesCMIP5 Projected Changes in the Annual Cycle of Precipitation in Monsoon Regionshttp://academiccommons.columbia.edu/catalog/ac:187382
Seth, Anji; Rauscher, Sara A.; Biasutti, Michela; Giannini, Alessandra; Camargo, Suzana J.; Rojas, Maisahttp://dx.doi.org/10.7916/D8T72GMHWed, 22 Jul 2015 16:21:35 +0000Analyses of phase 5 of the Coupled Model Intercomparison Project (CMIP5) experiments show that the global monsoon is expected to increase in area, precipitation, and intensity as the climate system responds to anthropogenic forcing. Concurrently, detailed analyses for several individual monsoons indicate a redistribution of rainfall from early to late in the rainy season. This analysis examines CMIP5 projected changes in the annual cycle of precipitation in monsoon regions, using a moist static energy framework to evaluate competing mechanisms identified to be important in precipitation changes over land. In the presence of sufficient surface moisture, the local response to the increase in downwelling energy is characterized by increased evaporation, increased low-level moist static energy, and decreased stability with consequent increases in precipitation. A remote mechanism begins with warmer oceans and operates on land regions via a warmer tropical troposphere, increased stability, and decreased precipitation. The remote mechanism controls the projected changes during winter, and the local mechanism controls the switch to increased precipitation during summer in most monsoon regions. During the early summer transition, regions where boundary layer moisture availability is reduced owing to decreases in evaporation and moisture convergence experience an enhanced convective barrier. Regions characterized by adequate evaporation and moisture convergence do not experience reductions in early summer precipitation.This enhanced convective barrier leads to a redistribution of rainfall from early to late summer, and is robust in the American and African monsoons but muddled in Asia. As described here, viewing monsoons from their inherent ties to the annual cycle could help to fingerprint changes as they evolve.Climate change, Atmospheric sciences, Hydrologic sciencesmb2415, arg25, sjc71Lamont-Doherty Earth Observatory, International Research Institute for Climate and SocietyArticlesNorth American Climate in CMIP5 Experiments. Part II: Evaluation of Historical Simulations of Intraseasonal to Decadal Variabilityhttp://academiccommons.columbia.edu/catalog/ac:187379
Sheffield, Justin; Camargo, Suzana J.; Fu, Rong; Hu, Qi; Jiang, Xianan; Johnson, Nathaniel; Karnauskas, Kristopher B.; Kim, Seon Tae; Kinter, Jim; Kumar, Sanjiv; Langenbrunner, Baird; Maloney, Eric; Mariotti, Annarita; Meyerson, Joyce E.; Neelin, J. David; Nigam, Sumant; Pan, Zaitao; Ruiz-Barradas, Alfredo; Seager, Richard; Serra, Yolande L.; Sun, De-Zheng; Wang, Chunzai; Xie, Shang-Ping; Yu, Jin-Yi; Zhang, Tao; Zhao, Minghttp://dx.doi.org/10.7916/D83R0S3DWed, 22 Jul 2015 15:06:49 +0000This is the second part of a three-part paper on North American climate in phase 5 of the Coupled Model Intercomparison Project (CMIP5) that evaluates the twentieth-century simulations of intraseasonal to multidecadal variability and teleconnections with North American climate. Overall, the multimodel ensemble does reasonably well at reproducing observed variability in several aspects, but it does less well at capturing observed teleconnections, with implications for future projections examined in part three of this paper. In terms of intraseasonal variability, almost half of the models examined can reproduce observed variability in the eastern Pacific and most models capture the midsummer drought over Central America. The multimodel mean replicates the density of traveling tropical synoptic-scale disturbances but with large spread among the models. On the other hand, the coarse resolution of the models means that tropical cyclone frequencies are underpredicted in the Atlantic and eastern North Pacific. The frequency and mean amplitude of ENSO are generally well reproduced, although teleconnections with North American climate are widely varying among models and only a few models can reproduce the east and central Pacific types of ENSO and connections with U.S. winter temperatures. The models capture the spatial pattern of Pacific decadal oscillation (PDO) variability and its influence on continental temperature and West Coast precipitation but less well for the wintertime precipitation. The spatial representation of the Atlantic multidecadal oscillation (AMO) is reasonable, but the magnitude of SST anomalies and teleconnections are poorly reproduced. Multidecadal trends such as the warming hole over the central-southeastern United States and precipitation increases are not replicated by the models, suggesting that observed changes are linked to natural variability.Climate change, Atmospheric sciences, Hydrologic sciencessjc71, rs229Lamont-Doherty Earth ObservatoryArticlesExtreme Storm Surge Hazard Estimation and Windstorm Vulnerability Assessment for Quantitative Risk Analysishttp://academiccommons.columbia.edu/catalog/ac:186995
Lopeman, Madeleine Elisehttp://dx.doi.org/10.7916/D8BC3XNRThu, 07 May 2015 00:24:18 +0000Quantification of risk to natural disasters is a valuable endeavor from engineering, policy and (re)insurance perspectives. This work presents two research efforts relating to meteorological risk, specifically with regard to storm surge hazard estimation and wind vulnerability assessment.
While many high water level hazard estimation methods have been presented in the literature and used in industry applications, none bases its results on disaggregated tidal gauge data while also capturing the effects of the evolution of storm surge over the duration of a storm. Additionally, the coastal destruction wreaked by Hurricane Sandy in 2012 prompted motivation to estimate the event’s return period. To that end, this dissertation first presents the motivation for and development of the clustered separated peaks-over-threshold simulation (CSPS) method, a novel approach to the estimation of high water level return periods at coastal locations. The CSPS uses a Monte Carlo simulation of storm surge activity based on statistics derived from tidal gauge data. The data are separated into three independent components (storm surge, tidal cycle and sea level rise) because different physical processes govern different components of water level. Peak storm surge heights are fit to the generalized Pareto distribution, chosen for its ability to fit a wide tail to limited data, and a clustering algorithm incorporates the evolution of storm surge over surge duration. Confidence intervals on the return period estimates are computed by applying the bootstrapping method to the storm surge data.
Two case studies demonstrate the application of the CSPS to coastal tidal gauge data. First, the CSPS is applied to tidal gauge data from lower Manhattan. The results suggest that the return period of Hurricane Sandy’s peak water level is 103 years (95% confidence interval 38–452 years). That the CSPS estimate is significantly lower than previously published return periods indicates that storm surge hazard in the New York Harbor has, until now, been underestimated. The CSPS is also applied to all tidal gauge stations managed by the National Oceanographic and Atmospheric Administration (NOAA) for which the hourly water level time histories are at least 30 years long. Comparison to NOAA’s exceedance probability levels for these stations suggests that the CSPS estimates higher return levels than NOAA, but also that the NOAA values fall within the 95% CI from the CSPS for more than half of the stations tested.
This dissertation continues with a critical comparison of windstorm vulnerability models. The intent of this research is to provide a compendium of reference curves against which to compare damage curves used in the reinsurance industry. The models tend to represent specific types of construction and use varying characteristic wind speed measurements to represent storm intensity. Wind speed conversion methods are used to harmonize wind speed scales. The different vulnerability models analyzed stem from different datasets and hypotheses, thus rendering them relevant to certain geographies or structural typologies. The resulting collection of comparable windstorm vulnerability models can serve as a reference framework against which damage curves from catastrophe risk models can be evaluated.Civil engineering, Hydrologic sciences, StatisticsCivil Engineering and Engineering MechanicsDissertationsMoisture budget analysis of SST-driven decadal Sahel precipitation variability in the twentieth centuryhttp://academiccommons.columbia.edu/catalog/ac:182102
Pomposi, Catherine A.; Kushnir, Yochanan; Giannini, Alessandrahttp://dx.doi.org/10.7916/D86W98XPMon, 02 Feb 2015 00:00:00 +0000It is well known that the Sahel region of Africa is impacted by decadal scale variability in precipitation, driven by global sea surface temperatures. This work demonstrates that the National Center for Atmospheric Research’s Community Atmosphere Model, version 4 is capable of reproducing relationships between Sahelian precipitation variability and Indian and Atlantic Ocean sea surface temperature variations on such timescales. Further analysis then constructs a moisture budget breakdown using model output and shows that the change in precipitation minus evaporation in the region is dominated by column integrated moisture convergence due to the mean flow, with the convergence of mass in the atmospheric column mainly responsible. It is concluded that the oceanic forcing of atmospheric mass convergence and divergence to a first order explains the moisture balance patterns in the region. In particular, the anomalous circulation patterns, including net moisture divergence by the mean and transient flows combined with negative moisture advection, together explain the drying of the Sahel during the second half of the twentieth century. Diagnosis of moisture budget and circulation components within the main rainbelt and along the monsoon margins show that changes to the mass convergence are related to the magnitude of precipitation that falls in the region, while the advection of dry air is associated with the maximum latitudinal extent of precipitation.Hydrologic sciences, Atmospheric sciences, Meteorologycap2203, yk16, arg25Lamont-Doherty Earth Observatory, International Research Institute for Climate and Society, Earth and Environmental SciencesArticlesRadiative convective equilibrium over a land surfacehttp://academiccommons.columbia.edu/catalog/ac:178573
Rochetin, Nicolas; Lintner, Benjamin R.; Findell, Kirsten L.; Sobel, Adam H.; Gentine, Pierrehttp://dx.doi.org/10.7916/D8CJ8C3WTue, 14 Oct 2014 00:00:00 +0000Radiative-convective equilibrium (RCE) describes an idealized state of the atmosphere in which the vertical temperature profile is determined by a balance between radiative and convective fluxes. While RCE has been applied extensively over oceans, its application over the land surface has been limited. The present study explores the properties of RCE over land using an atmospheric single column model (SCM) from the Laboratoire de Meteorologie Dynamique (LMD) General Circulation Model (LMDZ5B) coupled in temperature and moisture to a land surface model comprising a simplified bucket model with finite moisture capacity. Given the presence of a large-amplitude diurnal heat flux cycle, the resultant RCE exhibits multiple equilibria when conditions are neither strictly water- nor energy-limited. By varying top-of-the-atmosphere insolation (through changes in latitude), total system water content, and initial temperature conditions, the sensitivity of the land RCE states is assessed, with particular emphasis on the role of clouds. Based on this analysis, it appears that a necessary condition for the model to exhibit multiple equilibria is the presence of low-level clouds coupled to the diurnal cycle of radiation. In addition the simulated surface precipitation rate varies non-monotonically with latitude as a result of a tradeoff between in-cloud rain rate and subcloud rain re-evaporation, thus underscoring the importance of subcloud layer processes and unsaturated downdrafts. It is shown that clouds, especially at low levels, are key elements of the internal variability of the coupled land-atmosphere system through their feedback on radiation.Atmospheric sciences, Hydrologic sciences, Meteorologyahs129, pg2328Applied Physics and Applied Mathematics, Earth and Environmental Engineering, Earth and Environmental SciencesArticlesInterannual coupling between summertime surface temperature and precipitation: processes and implication for climate changehttp://academiccommons.columbia.edu/catalog/ac:178504
Berg, Alexis M.; Lintner, Benjamin R.; Findell, Kristen; Seneviratne, Sonia I.; van den Hurk, Bart; Ducharne, Agnes; Cheruy, Frederique; Hagemann, Stefan; Lawrence, David M.; Malyshev, Sergey; Meier, Arndt; Gentine, Pierrehttp://dx.doi.org/10.7916/D8TQ604SMon, 13 Oct 2014 00:00:00 +0000Widespread negative correlations between summertime-mean temperatures and precipitation over land regions are a well-known feature of terrestrial climate. This behavior has generally been interpreted in the context of soil moisture-atmosphere coupling, with soil moisture deficits associated with reduced rainfall leading to enhanced surface sensible heating and higher surface temperature. The present study revisits the genesis of these negative temperature- precipitation correlations using simulations from the Global Land-Atmosphere Coupling Experiment - Coupled Model Intercomparison Project phase 5 (GLACE-CMIP5) multi-model experiment. The analyses are based on simulations with 5 climate models, which were integrated with prescribed (non-interactive) and with interactive soil moisture over the period 1950-2100. While the results presented here generally confirm the interpretation that negative correlations between seasonal temperature and precipitation arise through the direct control of soil moisture on surface heat flux partitioning, the presence of widespread negative correlations when soil moisture- atmosphere interactions are artificially removed in at least two out of five models suggests that atmospheric processes, in addition to land surface processes, contribute to the observed negative temperature-precipitation correlation. On longer timescales, the negative correlation between precipitation and temperature is shown to have implications for the projection of climate change impacts on near surface climate: in all models, in the regions of strongest temperature-precipitation anti-correlation on interannual timescales, long-term regional warming is modulated to a large extent by the regional response of precipitation to climate change, with precipitation increases (decreases) being associated with minimum (maximum) warming. This correspondence appears to arise largely as the result of soil-moisture atmosphere interactions.Climate change, Hydrologic sciences, Atmospheric sciencesamb2393, pg2328International Research Institute for Climate and Society, Earth and Environmental EngineeringArticlesEstimating Effective Soil Hydraulic Properties Using Spatially Distributed Soil Moisture and Evapotranspirationhttp://academiccommons.columbia.edu/catalog/ac:177552
Shin, Yongchul; Mohanty, Binayak P.; Ines, Amor Valeriano M.http://dx.doi.org/10.7916/D8765CVXMon, 22 Sep 2014 00:00:00 +0000With the development of many earth-observing remote sensing (RS) platforms, spatially distributed remote sensing products are becoming critical inputs to many hydrologic and meteorological models. Remotely sensed soil moisture (SM) and evapotranspiration (ET) including ground-based data have the potential to be used for estimating pixel-scale soil hydraulic parameters. However, only a few studies have been conducted to better understand the impact of assimilating both SM and ET in estimating soil hydraulic properties of the root zone. In this study, we used inverse modeling based on the Noisy Monte Carlo Genetic Algorithm by linking RS SM and ET derived from the Surface Energy Balance Algorithm for Land for estimating pixel-scale effective soil hydraulic properties. Walnut Creek (Iowa), Brown (Illinois), and Lubbock (Texas) test sites were selected to assess the performance of this approach from point to satellite scales using synthetic and validation experiments. For comparison purposes, inverse modeling results were analyzed under three scenarios (ET only, SM only, and SM + ET in the optimization criteria). These results showed that considering both SM and ET components improved the estimations of effective soil hydraulic properties and reduced their uncertainties better than SM or ET only. Overall, although uncertainty exists, our proposed SM + ET based scheme performed well in estimating effective soil hydraulic properties at multiple spatial scales (point, airborne, and satellite footprints) under various hydroclimatic conditions.Environmental science, Hydrologic sciencesavi2101International Research Institute for Climate and SocietyArticlesUpdated coincident Ground and MODIS cloud Observations (2005-2011): Senator Beck and Swamp Angel study plots, Southwestern Coloradohttp://academiccommons.columbia.edu/catalog/ac:177386
Naud, Catherine M.; Rangwala, Imtiazhttp://dx.doi.org/10.7916/D8W957QDThu, 18 Sep 2014 00:00:00 +0000Data Format: NETCDF These two files include only the coincident hourly observations from ground and satellite (MODIS) at the Senator Beck and Swamp Angel sites. The ground data are described and obtained from the Center for Snow and Avalanche Studies (http://www.snowstudies.org/). the MODIS (MOD06 and MYD06) cloud data were obtained from the GSFC LAADS website (http://ladsweb.nascom.nasa.gov/data/search.html). There are generally two observations per day. Day and night flag is also assigned to the data. The satellite observations included here are: (1) cloud fraction and (2) cloud optical depth (during overcast and daylight conditions only).Atmospheric sciences, Meteorology, Hydrologic sciencescn2140Applied Physics and Applied MathematicsDatasetsA matter of divergence: Tracking recent warming at hemispheric scales using tree ring datahttp://academiccommons.columbia.edu/catalog/ac:176908
Wilson, R.; D'Arrigo, Rosanne Dorothy; Buckley, Brendan M.; Buntgen, U.; Esper, J.; Frank, D.; Luckman, B.; Payette, S.; Vose, R.; Youngblut, D.http://dx.doi.org/10.7916/D8KP80GHTue, 02 Sep 2014 00:00:00 +0000No current tree ring (TR) based reconstruction of extratropical Northern Hemisphere (ENH) temperatures that extends into the 1990s captures the full range of late 20th century warming observed in the instrumental record. Over recent decades, a divergence between cooler reconstructed and warmer instrumental large-scale temperatures is observed. We hypothesize that this problem is partly related to the fact that some of the constituent chronologies used for previous reconstructions show divergence against local temperatures in the recent period. In this study, we compiled TR data and published local/regional reconstructions that show no divergence against local temperatures. These data have not been included in other large-scale temperature reconstructions. Utilizing this data set, we developed a new, completely independent reconstruction of ENH annual temperatures (1750–2000). This record is not meant to replace existing reconstructions but allows some degree of independent validation of these earlier studies as well as demonstrating that TR data can better model recent warming at large scales when careful selection of constituent chronologies is made at the local scale. Although the new series tracks the increase in ENH annual temperatures over the last few decades better than any existing reconstruction, it still slightly under predicts values in the post-1988 period. We finally discuss possible reasons why it is so difficult to model post-mid-1980s warming, provide some possible alternative approaches with regards to the instrumental target and detail several recommendations that should be followed in future large-scale reconstruction attempts that may result in more robust temperature estimates.Paleoclimate science, Hydrologic sciencesrd5, bmb1Lamont-Doherty Earth ObservatoryArticlesA tree-ring based reconstruction of Logan River streamflow, northern Utahhttp://academiccommons.columbia.edu/catalog/ac:176903
Allen, Eric B.; Rittenour, Tammy M.; DeRose, R. Justin; Bekker, Matthew F.; Kjelgren, Roger; Buckley, Brendan M.http://dx.doi.org/10.7916/D8V40SJVTue, 02 Sep 2014 00:00:00 +0000We created six new tree-ring chronologies in northern Utah, which were used with preexisting chronologies from Utah and western Wyoming to reconstruct mean annual flow for the Logan River, the largest tributary of the regionally important Bear River. Two reconstruction models were developed, a “Local” model that incorporated two Rocky Mountain juniper chronologies located within the basin, and a “Regional” model that also included limber pine and pinyon pine chronologies from a larger area. The Local model explained 48.2% of the variability in the instrumental record and the juniper chronologies better captured streamflow variability than Douglas-fir collected within the Logan basin. Incorporating chronologies from the northern and southern margins of the transition zone of the western precipitation dipole increased the skill of the Regional model (r2 = 0.581). We suggest the increased Regional model skill indicates that both nodes of the western precipitation dipole influence northern Utah climate. The importance of Rocky Mountain juniper in both reconstructions of streamflow for this region suggests that future work should target these trees where more traditionally desirable species are not present. The reconstructions provide the first extended record of streamflow in northern Utah. Preinstrumental streamflows (1605–1921) exhibited considerable variability when compared to the instrumental period (1922–2005). Our findings confirm that the inherent uncertainty in contemporary water management and planning in the region is due to hydroclimatic variability that has persisted for at least the last four centuries.Paleoclimate science, Hydrologic sciencesbmb1Lamont-Doherty Earth ObservatoryArticlesA 576-Year Weber River Streamflow Reconstruction from Tree Rings for Water Resource Risk Assessment in the Wasatch Front, Utahhttp://academiccommons.columbia.edu/catalog/ac:176906
Bekker, Matthew F.; DeRose, R. Justin; Buckley, Brendan M.; Kjelgren, Roger; Gill, Nathan S.http://dx.doi.org/10.7916/D8QF8R5DTue, 02 Sep 2014 00:00:00 +0000We present a 576-year tree-ring-based reconstruction of streamflow for northern Utah's Weber River that exhibits considerable interannual and decadal-scale variability. While the 20th Century instrumental period includes several extreme individual dry years, it was the century with the fewest such years of the entire reconstruction. Extended droughts were more severe in duration, magnitude, and intensity prior to the instrumental record, including the most protracted drought of the record, which spanned 16 years from 1703 to 1718. Extreme wet years and periods are also a regular feature of the reconstruction. A strong early 17th Century pluvial exceeds the early 20th Century pluvial in magnitude, duration, and intensity, and dwarfs the 1980s wet period that caused significant flooding along the Wasatch Front. The long-term hydroclimatology of northern Utah is marked by considerable uncertainty; hence, our reconstruction provides water managers with a more complete record of water resource variability for assessment of the risk of droughts and floods for one of the largest and most rapidly growing population centers in the Intermountain West.Paleoclimate science, Hydrologic sciencesbmb1Lamont-Doherty Earth ObservatoryArticlesTree-ring reconstruction of the level of Great Salt Lake, USAhttp://academiccommons.columbia.edu/catalog/ac:176878
DeRose, R. Justin; Wang, Shih-Yu; Buckley, Brendan M.; Bekker, Matthew F.http://dx.doi.org/10.7916/D8ZW1J7TFri, 29 Aug 2014 00:00:00 +0000Utah’s Great Salt Lake (GSL) is a closed-basin remnant of the larger Pleistocene-age Lake Bonneville. The modern instrumental record of the GSL-level (i.e. elevation) change is strongly modulated by Pacific Ocean coupled ocean/atmospheric oscillations at low frequency, and therefore reflects the decadal-scale wet/dry cycles that characterize the region. A within-basin network of seven tree-ring chronologies was developed to reconstruct the GSL water year (September–August) level, based upon the instrumental record of GSL level from 1876 to 2005. The result was a 576-year reconstruction of the GSL level that extends from 1429 to 2005; all calibration-verification tests commonly used in dendroclimatology were passed. The reconstruction explains 48% of the variance in the instrumental GSL level and exhibits significant periodicity at sub-decadal scales over the past six centuries. Meanwhile, predominance of multi-decadal periodicity in the early half of the record shifted to quasi-decadal dominance in the latter half, and this is consistent with that of proxy reconstructions of the Pacific Decadal Oscillation. The GSL-level reconstruction is a crucial component to improving our insight into the possible controls of coupled ocean-atmosphere interactions on precipitation delivery.Paleoclimate science, Hydrologic sciencesbmb1Lamont-Doherty Earth ObservatoryArticlesHydroclimatology of Extreme Precipitation and Floods Originating from the North Atlantic Oceanhttp://academiccommons.columbia.edu/catalog/ac:177151
Nakamura, Jennifer Annehttp://dx.doi.org/10.7916/D86H4FM1Fri, 15 Aug 2014 00:00:00 +0000This study explores seasonal patterns and structures of moisture transport pathways from the North Atlantic Ocean and the Gulf of Mexico that lead to extreme large-scale precipitation and floods over land. Storm tracks, such as the tropical cyclone tracks in the Northern Atlantic Ocean, are an example of moisture transport pathways. In the first part, North Atlantic cyclone tracks are clustered by the moments to identify common traits in genesis locations, track shapes, intensities, life spans, landfalls, seasonal patterns, and trends. The clustering results of part one show the dynamical behavior differences of tropical cyclones born in different parts of the basin. Drawing on these conclusions, in the second part, statistical track segment model is developed for simulation of tracks to improve reliability of tropical cyclone risk probabilities. Moisture transport pathways from the North Atlantic Ocean are also explored though the specific regional flood dynamics of the U.S. Midwest and the United Kingdom in part three of the dissertation. Part I. Classifying North Atlantic Tropical Cyclones Tracks by Mass Moments. A new method for classifying tropical cyclones or similar features is introduced. The cyclone track is considered as an open spatial curve, with the wind speed or power information along the curve considered as a mass attribute. The first and second moments of the resulting object are computed and then used to classify the historical tracks using standard clustering algorithms. Mass moments allow the whole track shape, length and location to be incorporated into the clustering methodology. Tropical cyclones in the North Atlantic basin are clustered with K-means by mass moments producing an optimum of six clusters with differing genesis locations, track shapes, intensities, life spans, landfalls, seasonality, and trends. Even variables that are not directly clustered show distinct separation between clusters. A trend analysis confirms recent conclusions of increasing tropical cyclones in the basin over the past two decades. However, the trends vary across clusters. Part II: Tropical cyclone Intensity and Track Simulator (HITS) with Atlantic Ocean Applications for Risk Assessment. A nonparametric stochastic model is developed and tested for the simulation of tropical cyclone tracks. Tropical cyclone tracks demonstrate continuity and memory over many time and space steps. Clusters of tracks can be coherent, and the separation between clusters may be marked by geographical locations where groups of tracks diverge due to the physics of the underlying process. Consequently, their evolution may be non-Markovian. Markovian simulation models, as often used, may produce tracks that potentially diverge or lose memory quicker than nature. This is addressed here through a model that simulates tracks by randomly sampling track segments of varying length, selected from historical tracks. For performance evaluation, a spatial grid is imposed on the domain of interest. For each grid box, long-term tropical cyclone risk is assessed through the annual probability distributions of the number of storm hours, landfalls, winds, and other statistics. Total storm length is determined at birth by local distribution, and movement to other tropical cyclone segments by distance to neighbor tracks, comparative vector, and age of track. An assessment of the performance for tropical cyclone track simulation and potential directions for the improvement and use of such model are discussed. Part III: Dynamical Structure of Extreme Floods in the U.S. Midwest and the United Kingdom. Twenty extreme spring floods that occurred in the Ohio Basin between 1901 and 2008, identified from daily river discharge data, are investigated and compared to the April 2011 Ohio River flood event. Composites of synoptic fields for the flood events show that all these floods are associated with a similar pattern of sustained advection of low-level moisture and warm air from the tropical Atlantic Ocean and the Gulf of Mexico. The typical flow conditions are governed by an anomalous semi-stationary ridge situated east of the US East Coast, which steers the moisture and converges it into the Ohio Valley. Significantly, the moisture path common to all the 20 cases studied here as well as the case of April 2011 is distinctly different from the normal path of Atlantic moisture during spring, which occurs further west. It is shown further that the Ohio basin moisture convergence responsible for the floods is caused primarily by the atmospheric circulation anomaly advecting the climatological mean moisture field. Transport and related convergence due to the covariance between moisture anomalies and circulation anomalies are of secondary but non-negligible importance. The importance of atmospheric circulation anomalies to floods is confirmed by conducting a similar analysis for a series of winter floods on the River Eden in northwest England.Atmospheric sciences, Hydrologic sciences, Statisticsjam148Earth and Environmental EngineeringDissertationsAlternative Metrics of Green Roof Hydrologic Performance: Evapotranspiration and Peak Flow Reductionhttp://academiccommons.columbia.edu/catalog/ac:185821
Marasco, Danielhttp://dx.doi.org/10.7916/D89G5JZQMon, 07 Jul 2014 00:00:00 +0000Stormwater runoff presents an issue for many urban areas, triggering sewer overflows and water body pollution. Green roofs, engineered vegetative systems that replicate the stormwater absorption properties of natural landscapes, have become an attractive strategy for attenuating stormwater runoff. Historically, green roof hydrologic research has been focused on stormwater volume retention with less emphasis on evapotranspiration (ET) and stormwater detention. ET is associated with green roof environmental benefits, including stormwater runoff attenuation and urban heat island mitigation, and is an important parameter in hydrologic and energy models. Stormwater detention limits flow rate of stormwater into sewer systems, reducing the chance of sewer overflow. The aim of this research is to investigate green roof ET and stormwater detention behavior and develop methods to predict performance based on readily available environmental data. In order to study these hydrologic performance metrics, a series of four New York City green roofs were instrumented with sensors to measure rainfall, runoff, ET, and other environmental data. The green roofs span several extensive green roof installation types, specifically the vegetated mat, built-in-place, and modular tray systems. Environmental monitoring for this analysis began in January 2009 and concluded in October 2013. In the first study, a dynamic chamber method was developed to conduct high-resolution measurements of ET. Results show that monthly ET depths range from 2.2 to 153.6 mm. Chamber results were compared to two ET estimation methods, specifically the Penman-Monteith equation and an energy balance model. Dynamic chamber results were similar to Penman-Monteith estimates; however, the Penman-Monteith equation over-predicted bottommost ET fluxes during the winter, and under-predicted peak summer fluxes. In the second study, dynamic chamber measurements were used to investigate green roof behavior and the effectiveness of various predictive models, particularly in water-limited conditions. Comparison of Hargreaves, Priestley-Taylor, Penman, and Penman-Monteith equation results to chamber measurements reveals that the Priestley-Taylor equation best estimates ET. However, the Priestley-Taylor equation can still overestimate lower fluxes and underestimate high fluxes. Application of a storage model, antecedent precipitation index, and advection-aridity model indicates that the antecedent precipitation index best estimates ET in water-stressed conditions. In the third study, 501 rainfall events were used to characterize green roof stormwater detention behavior, through analysis of event peak rainfall rate reductions. Empirical models relating event peak runoff rate to rainfall depth and peak rainfall rate were developed. Roof-specific models allow for the comparison of peak reduction behavior among roofs, while a combined model allows for designers to estimate green roof event peak rainfall reduction performance. Model application shows that the modular tray system is most effective at reducing peak rainfall rate. Overall, this research provides valuable insight into green roof hydrologic performance. Analysis of environmental data reveals not only the ET and peak rainfall rate reduction performance of green roofs, but also the environmental factors that affect performance. Additionally, predictive models for ET and peak runoff rate investigated in this dissertation can be valuable tools for researchers, practitioners, and policymakers to estimate green roof hydrologic performance.Civil engineering, Environmental engineering, Hydrologic sciencesdem2124Civil Engineering and Engineering MechanicsDissertationsUncertainty in paleohydrologic reconstructions from molecular δD valueshttp://academiccommons.columbia.edu/catalog/ac:174886
Polissar, Pratigya Jeremy; D'Andrea, William Josephhttp://dx.doi.org/10.7916/D8JW8C0JFri, 13 Jun 2014 00:00:00 +0000Compound-specific δD measurements can be used for quantitative estimation of source water δD values, a useful tracer for paleohydrologic changes. Such estimates have quantifiable levels of uncertainty that are often miscalculated, resulting in inaccurate error reporting in the scientific literature that can impact paleohydrologic interpretations. Here, we summarize the uncertainties inherent to molecular δD measurements and the quantification of source water δD values, and discuss the assumptions involved when omitting various sources of uncertainty. Using standard protocols from measurement science, we derive the equations necessary to quantify these various sources of uncertainty. We show that analytical uncertainty is usually improperly estimated and that after apparent fractionation between δD values of source water and molecule, normalization of data to the VSMOW scale introduces the largest amount of uncertainty. Lastly, to facilitate systematic error reporting we provide an Uncertainty Calculator spreadsheet to conveniently calculate uncertainty in δD measurements.Paleoclimate science, Hydrologic sciences, Geochemistrypjp2119, wjd2111Lamont-Doherty Earth ObservatoryArticlesSystematic along-axis tidal triggering of microearthquakes observed at 9°50′N East Pacific Risehttp://academiccommons.columbia.edu/catalog/ac:173403
Stroup, Danielle F.; Tolstoy, Maria; Crone, Timothy J.; Malinverno, Alberto; Bohnenstiehl, Delwayne R.; Waldhauser, Felixhttp://dx.doi.org/10.7916/D8610XF7Mon, 28 Apr 2014 00:00:00 +0000Hydrothermal fluid circulation at mid-ocean ridges facilitates the exchange of heat and chemicals between the oceans and the solid Earth, and supports chemosynthetic microbial and macro-faunal communities. The structure and evolution of newly formed oceanic crust plays a dominant role in controlling the character and longevity of hydrothermal systems; however, direct measurements of subsurface processes remain technologically challenging to obtain. Previous studies have shown that tidally-induced stresses within the subseafloor modulate both fluid flow and microearthquake origin times. In this study, we observe systematic along-axis variations between peak microearthquake activity and maximum predicted tidal extension beneath the hydrothermal vent site at 9°50′N East Pacific Rise. We interpret this systematic triggering to result from pore-pressure perturbations propagating laterally through the hydrothermal system. Based on our observations and a one-dimensional pore pressure perturbation model, we estimate bulk permeability at ∼10⁻¹³ to 10⁻¹² m² within layer 2B over a calculated diffusive lengthscale of 2.0 km.Biological oceanography, Plate tectonics, Hydrologic sciencesmt290, tjc2129, amm4, drb34, fw2005Lamont-Doherty Earth ObservatoryArticlesOcean-atmosphere climate shift during the mid-to-late Holocene transitionhttp://academiccommons.columbia.edu/catalog/ac:172794
Morely, Audrey; Rosenthal, Yair; deMenocal, Peter B.http://dx.doi.org/10.7916/D82V2D6PFri, 28 Mar 2014 00:00:00 +0000Climate records of the mid-to-late Holocene transition, between 3–4 thousand years before present (ka), often exhibit a rapid change in response to the gradual change in orbital insolation. Here we investigate North Atlantic Central Water circulation as a possible mechanism regulating the latitudinal temperature gradient (LTG), which, in turn, amplifies climate sensitivity to small changes in solar irradiance. Through this mechanism, sharp climate events and transitions are the result of a positive feedback process that propagates and amplifies climate events in the North Atlantic region. We explore these linkages using an intermediate water temperature record reconstructed from Mg/Ca measurements of benthic foraminifera (Hyalinea balthica ) from a sediment core off NW Africa (889 m depth) between 0 to 5.5 ka. Our results show that Eastern North Atlantic Central Waters (ENACW) cooled by ~1°±0.7 °C~1°±0.7 °C and densities decreased by σθ=0.4±0.2σθ=0.4±0.2 between 3.3 and 2.6 ka. This shift in ENACW hydrography illustrates a transition towards enhanced mid-latitude atmospheric circulation after 2.7 ka in particular during cold events of the late-Holocene. The presented records demonstrate the important role of ENACW circulation in propagating the climate signatures of the LTG by reducing the meridional heat transfer from high to low latitudes during the transition from the Holocene Thermal Maximum to the late-Holocene. In addition, the dynamic response of ENACW circulation to the gradual climate forcing of LTGs provides a prime example of an amplifying climate feedback mechanism.Physical oceanography, Paleoclimate science, Hydrologic sciencespbd1Lamont-Doherty Earth ObservatoryArticlesImproving operational land surface model canopy evapotranspiration in Africa using a direct remote sensing approachhttp://academiccommons.columbia.edu/catalog/ac:171869
Marshall, M.; Tu, K.; Funk, C.; Michaelsen, Joel; Williams, A. Park; Williams, C.; Ardö , J.; Boucher, M.; Cappelaere, B.; de Grandcourt, A.; Nickless, A.; Nouvellon, Y.; Scholes, R.; Kutsch, W.http://dx.doi.org/10.7916/D84X55VRMon, 17 Mar 2014 00:00:00 +0000Climate change is expected to have the greatest impact on the world's economically poor. In the Sahel, a climatically sensitive region where rain-fed agriculture is the primary livelihood, expected decreases in water supply will increase food insecurity. Studies on climate change and the intensification of the water cycle in sub-Saharan Africa are few. This is due in part to poor calibration of modeled evapotranspiration (ET), a key input in continental-scale hydrologic models. In this study, a remote sensing model of transpiration (the primary component of ET), driven by a time series of vegetation indices, was used to substitute transpiration from the Global Land Data Assimilation System realization of the National Centers for Environmental Prediction, Oregon State University, Air Force, and Hydrology Research Laboratory at National Weather Service Land Surface Model (GNOAH) to improve total ET model estimates for monitoring purposes in sub-Saharan Africa. The performance of the hybrid model was compared against GNOAH ET and the remote sensing method using eight eddy flux towers representing major biomes of sub-Saharan Africa. The greatest improvements in model performance were at humid sites with dense vegetation, while performance at semi-arid sites was poor, but better than the models before hybridization. The reduction in errors using the hybrid model can be attributed to the integration of a simple canopy scheme that depends primarily on low bias surface climate reanalysis data and is driven primarily by a time series of vegetation indices.Climate change, Hydrologic sciencesapw2134Lamont-Doherty Earth ObservatoryArticlesAnalysis of Spectral Excitation for Measurements of Fluorescence Constituents in Natural Watershttp://academiccommons.columbia.edu/catalog/ac:169495
Chekalyuk, Alexander M.; Hafez, Mark A.http://dx.doi.org/10.7916/D8WS8R79Fri, 24 Jan 2014 00:00:00 +0000Field measurements of chlorophyll-a (Chl), phycoerythrin (PE), chromophoric dissolved organic matter (CDOM), and variable fluorescence (Fv/Fm) in diverse waters of the California Current, Mediterranean Sea and Gulf of Mexico using 375, 405, 510 and 532 nm laser excitation wavelengths (EW) are analyzed. EW = 375 and 405 nm were found more suitable for Chl assessment in high-Chl (greater than 10 μg/l) waters. Both EW = 532 and 510 nm can be used to efficiently stimulate PE fluorescence for structural characterization of phytoplankton communities. EW = 375 nm and 405 nm can provide best results for CDOM assessments in offshore oceanic waters; the green EWs can be also used for CDOM measurements in fresh and estuarine water types in conjunction with spectral discrimination between CDOM and PE fluorescence. Both EW = 405 and 510 are suitable for photo-physiological Fv/Fm assessments, though using EW = 405 nm may result in underestimation of PE-containing phytoplankton groups present in mixed phytoplankton assemblages.Hydrologic sciences, Opticsac2709, mh3170Lamont-Doherty Earth ObservatoryArticlesLate Quaternary Sedimentary Record and Holocene Channel Avulsions of the Jamuna and Old Brahmaputra River Valleys in the Upper Bengal Delta Plainhttp://academiccommons.columbia.edu/catalog/ac:168954
Pickering, Jennifer L.; Goodbred, Steven L.; Reitz, Meredith Dorothy; Hartzog, Thomas R.; Mondal, Dhiman R.; Hossain, Md. Saddamhttp://dx.doi.org/10.7916/D8QC01FKWed, 22 Jan 2014 00:00:00 +0000The first Holocene stratigraphic record of river-channel occupation and switching between the Brahmaputra–Jamuna and Old Brahmaputra paleovalleys is presented here. Motivated by the Brahmaputra River's historic avulsion from the Old Brahmaputra channel to its present-day Jamuna course, we have obtained sediment and radiocarbon samples from 41 boreholes along a 120 km transect crossing these two braided-river valleys. The stratigraphy along this transect reveals sand-dominated Holocene channel systems, each bound by remnant, mud-capped Pleistocene stratigraphy. Using sediment lithology and bulk strontium concentration as a provenance indicator, we define the geometry and channel-occupation history of each paleovalley. The western Brahmaputra–Jamuna valley is broad and somewhat deeper compared with the Old Brahmaputra valley, the latter actually comprising a composite of two narrower sub-valleys bifurcated by an antecedent topographic remnant. The gently sloped valley margins (slope: 0.002 to 0.007) and high width-to-thickness ratio (W/T: ~ 1000) of the Brahmaputra–Jamuna valley suggest that it was filled primarily through lateral channel migration and the reworking of braidbelt and overbank deposits. Conversely, the two Old Brahmaputra sub-valleys have comparatively steeper valley margins (slope: 0.007 to 0.022) and lower width-to-thickness ratios (W/T: ~ 125 and ~ 250), indicating that these were filled primarily through vertical aggradation of channel sands. We attribute this disparity in valley geometry and fill processes to the different occupation histories for each valley. In this case, the much larger Brahmaputra–Jamuna valley represents the principal, if not singular, river course during the last lowstand of sea-level, with a prominent gravel lag underlying the valley. In contrast the smaller Old Brahmaputra valleys do not appear to have been present, or at least well developed, at the last lowstand. Rather these courses were first occupied during the early Holocene transgression, and we infer that the river had been previously excluded from this region by the relatively higher elevation between the Madhupur Terrace and the Shillong Massif. We also demonstrate that the Brahmaputra River experienced 3–4 major avulsions during the Holocene, with considerably longer occupation times within the principal Brahmaputra–Jamuna valley. Together these observations indicate that occupation history and antecedent topography have been important controls on river course mobility and avulsion behavior.Geomorphology, Hydrologic sciences, Geologymdr2152Lamont-Doherty Earth ObservatoryArticlesA multispecies tree ring reconstruction of Potomac River streamflow (950–2001)http://academiccommons.columbia.edu/catalog/ac:167937
Maxwell, R. Stockton; Hessl, Amy E.; Cook, Edward R.; Pederson, Neilhttp://dx.doi.org/10.7916/D8Z31WKHTue, 03 Dec 2013 00:00:00 +0000Mean May–September Potomac River streamflow was reconstructed from 950–2001 using a network of tree ring chronologies (n = 27) representing multiple species. We chose a nested principal components reconstruction method to maximize use of available chronologies backward in time. Explained variance during the period of calibration ranged from 20% to 53% depending on the number and species of chronologies available in each 25 year time step. The model was verified by two goodness of fit tests, the coefficient of efficiency (CE) and the reduction of error statistic (RE). The RE and CE never fell below zero, suggesting the model had explanatory power over the entire period of reconstruction. Beta weights indicated a loss of explained variance during the 1550–1700 period that we hypothesize was caused by the reduction in total number of predictor chronologies and loss of important predictor species. Thus, the reconstruction is strongest from 1700–2001. Frequency, intensity, and duration of drought and pluvial events were examined to aid water resource managers. We found that the instrumental period did not represent adequately the full range of annual to multidecadal variability present in the reconstruction. Our reconstruction of mean May–September Potomac River streamflow was a significant improvement over the Cook and Jacoby (1983) reconstruction because it expanded the seasonal window, lengthened the record by 780 years, and better replicated the mean and variance of the instrumental record. By capitalizing on variable phenologies and tree growth responses to climate, multispecies reconstructions may provide significantly more information about past hydroclimate, especially in regions with low aridity and high tree species diversity.Paleoclimate science, Meteorology, Hydrologic scienceserc1, np150Lamont-Doherty Earth ObservatoryArticlesHydrometeorological Reconstructions for Northeastern Mongolia Derived from Tree Rings: 1651–1995http://academiccommons.columbia.edu/catalog/ac:167934
Pederson, Neil; Jacoby, Gordon; D'Arrigo, Rosanne Dorothy; Cook, Edward R.; Buckley, Brendan M.; Dugarjav, Chultemiin; Mijiddorj, R.http://dx.doi.org/10.7916/D82V2D1FTue, 03 Dec 2013 00:00:00 +0000Reconstructions of annual (prior August–current July) precipitation and streamflow, 345 yr in length (1651–1995), are presented for northeastern Mongolia based on tree-ring width data. These precipitation and streamflow reconstructions account for 54% and 48% of the respective variance in instrumental data over the past 50 years. Variations in instrumental precipitation and streamflow are within the range of those reconstructed over the length of tree-ring records. However, there appear to be more frequent extended wet periods during the twentieth century. Multitaper spectral analysis revealed statistically significant peaks at 10.8 and 12.8 yr for the precipitation reconstruction, and at 12.8 and 20.3–23.8 yr for the streamflow reconstruction. Similarly, singular spectrum analysis identified spectral modes of variation at 12 and 21 yr for both series. These spectra resemble those found for tree-ring-based precipitation reconstructions in central China as well as the western United States, and may reflect solar influences on the climate of Mongolia.Meteorology, Hydrologic sciences, Paleoclimate sciencenp150, gcj1, rd5, erc1, bmb1Lamont-Doherty Earth ObservatoryArticlesTemperature and precipitation in Mongolia based on dendroclimatic investigationshttp://academiccommons.columbia.edu/catalog/ac:167942
Jacoby, Gordon; Pederson, Neil; D'Arrigo, Rosanne Dorothyhttp://dx.doi.org/10.7916/D8JW8BTWTue, 03 Dec 2013 00:00:00 +0000Recent tree-ring studies in Mongolia provide evidence of unusual warming that is in agreement with large-scale reconstructed and recorded temperatures for the Northern Hemisphere and the Arctic. One Mongolian proxy record for temperature extends back over 1000 years and several others are over 350 years in length. Precipitation reconstructions based on tree rings reflect recent increases but also indicate that the increases are within the long-term range of variations. Spectral analyses of recorded precipitation data and the reconstructions support the hypotheses of quasi-solar periodicity in precipitation variation, previously suggested by others.Paleoclimate science, Meteorology, Hydrologic sciencesgcj1, np150, rd5Lamont-Doherty Earth ObservatoryArticlesA Combined Field And Laboratory Investigation Into The Transport Of Fecal Indicator Microorganisms Through A Shallow Drinking Water Aquifer In Bangladeshhttp://academiccommons.columbia.edu/catalog/ac:167221
Feighery, John E.http://dx.doi.org/10.7916/D8J1012NWed, 20 Nov 2013 00:00:00 +0000This dissertation presents an examination of the causes and mechanisms underlying the widespread contamination of a shallow groundwater aquifer by fecal bacteria. The context for this study is a field site located in a rural area of Bangladesh that represents a microcosm for the many challenges facing the approximately 2 billion people worldwide who rely upon groundwater for their daily needs. The unique contributions of this work include an improved numerical model for fitting column test results, a conceptual model to explain seasonal patterns of well contamination based on the hydraulic interaction of ponds and irrigation/drainage canals and a new understanding of the important role that such canals might play in predicting the microbial contamination of shallow aquifers in flood-protected areas. The mechanisms responsible for filtration of the fecal indicator bacteria, Escherichia coli, during passage through the fine sand aquifer were first investigated through laboratory column experiments using intact sediment cores from the field site as well as repacked sediment that had been dried and, in some experiments, chemically cleaned. To fit the hyper-exponential spatial profiles of attached bacteria in one third of the experiments, a finite difference two-population model with reversible and irreversible attachment modes incorporating bacterial die-off was developed. Where the two-population phenomenon was observed, one population typically was highly irreversible while the other was reversible with a smaller irreversible attachment rate. When applied to transport in the field, this model predicted only a two-fold reduction in bacterial concentrations over a distance of 10 m and transport was limited mainly by the bacterial die-off rate, which was also measured using microcosm experiments. The occurrence of the second population was associated with larger grain size and lower percentage of fine particles and the attachment rates in general increased linearly with increasing percentage of fines. Transport from contaminated surface water to nearby tubewells was studied in the field through measurements of bacterial infiltration below canals and ponds both inside and outside of the flood control embankment. A two-dimensional finite element model of the field-pond-canal system was built and fitted to heads measured at three monitoring wells and 2 surface water bodies. Using parameters from the field measurements, the model was not able to explain the seasonal pattern of E. coli concentrations in tubewells, even when reversible attachment assumptions from the column test results were applied. An alternative conceptual model that incorporates the seasonal shift in flow direction caused by the canal network was developed using the fitted finite element model and could explain the observed pattern of well contamination. The importance of the irrigation/drainage canals in determining the frequency of tubewell contamination by E. coli at the site was further demonstrated by applying a logistic regression model using the intensity of latrines, canals and ponds as predictors, after applying spatial decay rates drawn from the infiltration literature. The resulting Intensity Model found that population density, unsanitary latrines and canals together could explain 48% of the variation in the frequency of E. coli detection in tubewells, but these parameters were only significant at a low spatial decay rate (0.01 m-1). A less complex Proximity Model provides nearly the same explanatory power but only required population with 25 m and the distance to the nearest canal as predictors. These models could be useful in predicting water-related health risks, evaluating contamination risk for groundwater sources based on the sanitary environment around the well or estimating the potential benefits from improvements to sanitation infrastructure in a given region.Environmental science, Hydrologic sciences, Water resources managementjef2112Civil Engineering and Engineering Mechanics, Earth and Environmental EngineeringDissertationsInfluence of the Amazon River discharge on the biogeography of phytoplankton communities in the western tropical north Atlantichttp://academiccommons.columbia.edu/catalog/ac:177033
Goes, Joaquim I.; de Rosario Gomes, Helga; Chekalyuk, Alexander M.; Carpenter, Edward J.; Montoya, Joseph P.; Coles, Victoria J.; Yager, Patricia L.; Berelson, William M.; Capone, Douglas G.; Foster, Rachel A.; Steinberg, Deborah K.; Subramaniam, Ajit; Hafez, Mark A.http://hdl.handle.net/10022/AC:P:21824Thu, 26 Sep 2013 00:00:00 +0000An Advanced Laser Fluorometer (ALF) capable of discriminating several phytoplankton pigment types was utilized in conjunction with microscopic data to map the distribution of phytoplankton communities in the Amazon River plume in May–June-2010, when discharge from the river was at its peak. Cluster analysis and Non-metric Multi-Dimensional Scaling (NMDS) helped distinguish three distinct biological communities that separated largely on the basis of salinity gradients across the plume. These three communities included an “estuarine type” comprised of a high biomass mixed population of diatoms, cryptophytes and green-water Synechococcus spp. located upstream of the plume, a “mesohaline type” made up largely of communities of Diatom-Diazotroph Associations (DDAs) and located in the northwestern region of the plume and an “oceanic type” in the oligotrophic waters outside of the plume made up of Trichodesmium and Synechococcus spp. Although salinity appeared to have a substantial influence on the distribution of different phytoplankton groups, ALF and microscopic measurements examined in the context of the hydro-chemical environment of the river plume, helped establish that the phytoplankton community structure and distribution were strongly controlled by inorganic nitrate plus nitrite (NO3 + NO2) availability whose concentrations were low throughout the plume. Towards the southern, low-salinity region of the plume, NO3 + NO2 supplied by the onshore flow of subsurface (∼80 m depth) water, ensured the continuous sustenance of the mixed phytoplankton bloom. The large drawdown of SiO3 and PO4 associated with this “estuarine type” mixed bloom at a magnitude comparable to that observed for DDAs in the mesohaline waters, leads us to contend that, diatoms, cryptophytes and Synechococcus spp., fueled by the offshore influx of nutrients also play an important role in the cycling of nutrients in the Amazon River plume.Biology, Hydrologic sciencesjig2113, ac2709, as2498, mh3170Lamont-Doherty Earth ObservatoryArticlesScaling in Surface Hydrology: Progress and Challengeshttp://academiccommons.columbia.edu/catalog/ac:165839
Gentine, Pierre; Troy, Tara J.; Lintner, Benjamin R.; Findell, Kirsten L.http://hdl.handle.net/10022/AC:P:21826Thu, 26 Sep 2013 00:00:00 +0000This paper presents a review of the challenges in spatial and temporal scales in surface hydrology. Fundamental issues and gaps in our understanding of hydrologic scaling are highlighted and shown to limit predictive skill, with heterogeneities, nonlinearities, and non-local transport processes among the most significant difficulties faced in scaling. The discrepancy between the physical process scale and the measurement scale has played a major role in restricting the development of theories, for example, relating observational scales to scales of climate and weather models. Progress in our knowledge of scaling in hydrology requires systematic determination of critical scales and scale invariance of physical processes. In addition, viewing the surface hydrologic system as composed of interacting dynamical subsystems should facilitate the definition of scales observed in nature. Such an approach would inform the development of careful, resolution-dependent, physical law formulation based on mathematical techniques and physical laws.Hydrologic sciences, Applied mathematicspg2328Lamont-Doherty Earth Observatory, Earth and Environmental EngineeringArticlesEmergent relation between surface vapor conductance and relative humidity profiles yields evaporation rates from weather datahttp://academiccommons.columbia.edu/catalog/ac:166545
Salvucci, Guido D.; Gentine, Pierrehttp://hdl.handle.net/10022/AC:P:21815Thu, 26 Sep 2013 00:00:00 +0000The ability to predict terrestrial evapotranspiration (E) is limited by the complexity of rate-limiting pathways as water moves through the soil, vegetation (roots, xylem, stomata), canopy air space, and the atmospheric boundary layer. The impossibility of specifying the numerous parameters required to model this process in full spatial detail has necessitated spatially upscaled models that depend on effective parameters such as the surface vapor conductance (Csurf). Csurf accounts for the biophysical and hydrological effects on diffusion through the soil and vegetation substrate. This approach, however, requires either site-specific calibration of Csurf to measured E, or further parameterization based on metrics such as leaf area, senescence state, stomatal conductance, soil texture, soil moisture, and water table depth. Here, we show that this key, rate-limiting, parameter can be estimated from an emergent relationship between the diurnal cycle of the relative humidity profile and E. The relation is that the vertical variance of the relative humidity profile is less than would occur for increased or decreased evaporation rates, suggesting that land–atmosphere feedback processes minimize this variance. It is found to hold over a wide range of climate conditions (arid–humid) and limiting factors (soil moisture, leaf area, energy). With this relation, estimates of E and Csurf can be obtained globally from widely available meteorological measurements, many of which have been archived since the early 1900s. In conjunction with precipitation and stream flow, long-term E estimates provide insights and empirical constraints on projected accelerations of the hydrologic cycle.Environmental science, Hydrologic sciences, Biophysicspg2328Earth and Environmental EngineeringArticlesEquatorial Upwelling Enhances Nitrogen Fixation in the Atlantic Oceanhttp://academiccommons.columbia.edu/catalog/ac:167898
Subramaniam, Ajit; Mahaffey, Claire; Johns, William; Mahowald, NatalieThu, 26 Sep 2013 00:00:00 +0000Surface waters in upwelling regions are thought to be nutrient rich and hence inhibit nitrogen fixation (diazotrophy) because diazotrophs can preferentially assimilate nitrate and ammonia instead of expending energy to fix dinitrogen. We found average nitrogen fixation rates to be two to seven times higher in the surface waters of the upwelling region of the eastern equatorial Atlantic than typically measured here during non-upwelling periods. We posit that in this region, low nitrate-phosphate ratio waters are upwelled, and an initial bloom of non-diazotrophic phytoplankton removes recently upwelled nitrate. Thereby, diazotrophy is fuelled by residual phosphate and by a combination of aeolian and upwelled sources of iron. Annually, we estimate that approximately 47 Gmol of new nitrogen is introduced by diazotrophy in upwelled waters alone and 195 Gmol N is fixed in the equatorial Atlantic region. Our findings challenge the paradigm that the highest nitrogen fixation rates occur in oligotrophic gyres and instead provide evidence of its importance in upwelling regimes where phosphate- and iron-rich waters rich are upwelled.Hydrologic sciences, Chemical oceanographyas2498Lamont-Doherty Earth ObservatoryArticlesSurface and atmospheric controls on the onset of moist convection over landhttp://academiccommons.columbia.edu/catalog/ac:165719
Gentine, Pierre; Holtslag, Albert A. M.; D’Andrea, Fabio; Ek, Michaelhttp://hdl.handle.net/10022/AC:P:21792Wed, 25 Sep 2013 00:00:00 +0000The onset of moist convection over land is investigated using a conceptual approach with a slab boundary layer model. We here determine the essential factors for the onset of boundary layer clouds over land, and study their relative importance. They are: 1) the ratio of the temperature to the moisture lapse rates of the free troposphere, i.e. the inversion Bowen ratio, 2) the mean-daily surface temperature, 3) the relative humidity of the free troposphere and 4) the surface evaporative fraction. A clear transition is observed between two regimes of moistening of the boundary layer as assessed by the relative humidity at the boundary layer top. In the first so-called wet soil advantage regime, the moistening results from the increase of the mixed-layer specific humidity, which linearly depends on the surface evaporative fraction and inversion Bowen ratio through a dynamic boundary layer factor. In the second so-called dry soil advantage regime, the relative humidity tendency at the boundary layer top is controlled by the thermodynamics and changes in the moist adiabatic induced by the decreased temperature at the boundary layer top and consequent reduction in saturation water vapor pressure. This regime pertains for very deep boundary layers under weakly stratified free troposphere over hot surface conditions. In the context of the conceptual model, a rise in free-tropospheric temperature (global warming) increases the occurrence of deep convection and reduces the cloud cover over moist surfaces. This study provides new intuition and predictive capacity on the mechanism controlling the occurrence of moist convection over land.Hydrologic sciences, Meteorologypg2328Earth and Environmental EngineeringArticlesDepositional architecture, provenance, and tectonic/eustatic modulation of Miocene submarine fans in the Shikoku Basin: Results from Nankai Trough Seismogenic Zone Experimenthttp://academiccommons.columbia.edu/catalog/ac:168333
Pickering, Kevin T.; Underwood, Michael B.; Saito, Sanny; Naruse, Hajime; Kutterolf, Steffen; Scudder, Rachel; Park, Jin-Oh; Moore, Gregory F.; Slagle, Angela L.Wed, 25 Sep 2013 00:00:00 +0000Seismostratigraphy, coring, and logging while drilling during Integrated Ocean Drilling Program Expeditions 319, 322, and 333 (Sites C0011/C0012) show three Miocene submarine fans in the NE Shikoku Basin, with broadly coeval deposits at Ocean Drilling Program Site 1177 and Deep Sea Drilling Project Site 297 (NW Shikoku Basin). The sediment dispersal patterns have major implications for paleogeographies at that time. The oldest, finer-grained (Kyushu) fan has sheet-like geometry; quartz-rich flows were fed mostly from an ancestral landmass in the East China Sea. During prolonged hemipelagic mud deposition at C0011-C0012 (~12.2 to 9.1 Ma), sand supply continued at Sites 1177 and 297. Sand delivery to much of the Shikoku Basin halted during a phase of sinistral strike slip to oblique plate motion, after which the Daiichi Zenisu Fan (~9.1 to 8.0 Ma) was fed by submarine channels. The youngest fan (Daini Zenisu; ~8.0 to 7.6 Ma) has sheet-like geometry with thick-bedded, coarse-grained pumiceous sandstones. The pumice fragments were fed from a mixed provenance that included the collision zone of the Izu-Bonin and Honshu Arcs. The shift from channelized to sheet-like flows was favored by renewal of relatively rapid northward subduction, which accentuated the trench as a bathymetric depression. Increased sand supply appears to correlate with long-term eustatic lowstands of sea level. The stratigraphic position and 3-D geometry of the sandbodies have important implications for subduction-related processes, including the potential for focused fluid flow and fluid overpressures above and below the plate boundary fault: In sheet-like sands, pathways for fluid flow have greater horizontal permeability compared with those in channel sands.Hydrologic sciences, Petroleum geology, Plate tectonicsals207Lamont-Doherty Earth ObservatoryArticlesInterdependence of climate, soil, and vegetation as constrained by the Budyko curvehttp://academiccommons.columbia.edu/catalog/ac:165592
Gentine, Pierre; D'Odorico, Paolo; Lintner, Benjamin R.; Sivandran, Gajan; Salvucci, Guidohttp://hdl.handle.net/10022/AC:P:21749Fri, 20 Sep 2013 00:00:00 +0000The Budyko curve is an empirical relation among evapotranspiration, potential evapotranspiration and precipitation observed across a variety of landscapes and biomes around the world. Using data from more than three hundred catchments and a simple water balance model, the Budyko curve is inverted to explore the ecohydrological controls of the soil water balance. Comparing the results across catchments reveals that aboveground transpiration efficiency and belowground rooting structure have adapted to the dryness index and the phase lag between peak seasonal radiation and precipitation. The vertical and/or lateral extent of the rooting zone exhibits a maximum in semi-arid catchments or when peak radiation and precipitation are out of phase. This demonstrates plant strategies in Mediterranean climates in order to cope with water stress: the deeper rooting structure buffers the phase difference between precipitation and radiation. Results from this study can be used to constrain land-surface parameterizations in ungauged basins or general circulation models.Hydrologic sciences, Environmental sciencepg2328Earth and Environmental EngineeringArticlesEvidence of Silica Leakage to the Tropical Atlantic via Antarctic Intermediate Water during Marine Isotope Stage 4http://academiccommons.columbia.edu/catalog/ac:171577
Anderson, Robert F.; Griffiths, James D.; Barker, Stephen; Hendry, Katharine R.; Thornalley, David J. R.; van de Flierdt, Tina; Hall, Ian R.http://hdl.handle.net/10022/AC:P:21569Wed, 11 Sep 2013 00:00:00 +0000Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water (SAMW) are the main conduits for the supply of dissolved silica (silicic acid) from the deep Southern Ocean to the low latitude surface ocean, and therefore have an important control on low latitude diatom productivity. Enhanced supply of silicic acid by AAIW (and SAMW) during glacial periods may have enabled tropical diatoms to outcompete carbonate-producing phytoplankton, decreasing the relative export of inorganic to organic carbon to the deep ocean and lowering atmospheric CO2. This mechanism is known as the 'Silicic Acid Leakage Hypothesis' (SALH). Here we present records of neodymium and silicon isotopes from the western tropical Atlantic that provide the first direct evidence of increased silicic acid leakage from the Southern Ocean to the tropical Atlantic within AAIW during glacial Marine Isotope Stage (MIS) 4 (~60-80 ka). This leakage is coeval with enhanced diatom export in the NW Atlantic and across the eastern equatorial Atlantic and provides support for the SALH as a contributor to CO2 drawdown during full glacial development.Hydrologic sciencesrfa1Lamont-Doherty Earth ObservatoryArticlesCraters Hosting Radar-Bright Deposits in Mercury's North Polar Region: Areas of Persistent Shadow Determined from MESSENGER Imageshttp://academiccommons.columbia.edu/catalog/ac:164893
Chabot, Nancy L.; Ernst, Carolyn M.; Harmon, John K.; Murchie, Scott L.; Solomon, Sean C.; Blewett, David T.; Denevi, Brett W.http://hdl.handle.net/10022/AC:P:21527Thu, 05 Sep 2013 00:00:00 +0000Radar-bright features near Mercury's poles were discovered in Earth-based radar images and proposed to be water ice present in permanently shadowed areas. Images from MESSENGER's one-year primary orbital mission provide the first nearly complete view of Mercury’s north polar region, as well as multiple images of the surface under a range of illumination conditions. We find that radar-bright features near Mercury's north pole are associated with locations persistently shadowed in MESSENGER images. Within 10 degrees of the pole, almost all craters larger than 10 km in diameter host radar-bright deposits. There are several craters located near Mercury's north pole with sufficiently large diameters to enable long-lived water ice to be thermally stable at the surface within regions of permanent shadow. Craters located farther south also host radar-bright deposits and show a preference for cold-pole longitudes; thermal models suggest that a thin insulating layer is required to cover these deposits if the radar-bright material consists predominantly of longlived water ice. Many small (less than 10 km diameter) and low-latitude (extending southward to 66 degrees N) craters host radar-bright material, and water ice may not be thermally stable in these craters for ~1 Gy, even beneath an insulating layer. The correlation of radar-bright features with persistently shadowed areas is consistent with the deposits being composed of water ice, and future thermal modeling of small and low-latitude craters has the potential to further constrain the nature, source, and timing of emplacement of the radar-bright material.Hydrologic sciences, Planetologyscs2186Lamont-Doherty Earth ObservatoryArticlesDrainage through Subglacial Water Sheetshttp://academiccommons.columbia.edu/catalog/ac:164903
Creyts, Timothy T.; Schoof, Christian G.http://hdl.handle.net/10022/AC:P:21530Thu, 05 Sep 2013 00:00:00 +0000Subglacial drainage plays an important role in controlling coupling between glacial ice and underlying bed. Here, we study the flow of water in thin, macroporous sheets between ice and bed. Previous work shows that small perturbations in depth of a nearly parallel-sided water film grow unstably because these areas have enhanced viscous dissipation that leads to enhanced melting of an ice roof. We argue that in the presence of bed protrusions bridging a water sheet, downward motion of the ice roof can stabilize this sheet. Stability results when the rate of roof closure increases faster with water depth than the rate of viscous dissipation. We therefore modify existing theory to include protrusions that partially support the overlying glacier. Differences in the pressure on protrusions relative to water pressure drive roof closure. The mechanisms of both regelation and creep normal to the bed close the overlying ice roof and decrease the icebed gap. In order to account for multiple protrusion sizes along the bed (for instance, resulting from an assortment of various-sized sediment grains), we incorporate a method of partitioning overburden pressure among different protrusion size classes and the water sheet. Partitioning is dependent on the amount of ice protrusion contact and, therefore, water depth. This method allows prediction of roof closure rates. We then investigate stable, steady sheet configurations for reasonable parameter choices and find that these steady states can occur for modest water depths at very low effective pressures, as is appropriate for ice streams. Moreover, we find that multiple steady sheet thicknesses exist, raising the possibility of switches between low and high hydraulic conductivity regimes for the subglacial water system.Hydrologic sciencesttc2119Lamont-Doherty Earth ObservatoryArticlesHydraulics of Subglacial Supercooling: Theory and Simulations for Clear Water Flowshttp://academiccommons.columbia.edu/catalog/ac:164900
Creyts, Timothy T.; Clarke, Garry K. C.http://hdl.handle.net/10022/AC:P:21529Thu, 05 Sep 2013 00:00:00 +0000Glaciohydraulic supercooling is a mechanism for accreting ice and sediment to the base of glaciers. We extend existing models by reworking the Spring‐Hutter model for subglacial water flow in tubular conduits to allow for distributed water sheets. Our goal is to determine diagnostic features of supercooling relative to controlling variables. Results focus on along‐path water flow under time‐varying conditions, with attention to ice accretion in and along subglacial overdeepenings. We contrast simulations with constant recharge to diurnally‐varying recharge and expose behavior that cannot be inferred from simple models. For example, locations of simulated ice accretion differ from those found for steady state models, even though total ice accretion remains comparable to field estimates. Downstream accretion influences upstream effective pressures that then modify the hydraulic gradient that drives water flow. This modified gradient tends to inhibit additional accretion by increasing velocity and heat production via viscous dissipation. During diurnal cycles, accretion varies considerably: in daytime, viscous dissipation dominates the heat balance and ice melts. In morning and evening, when flow is rising or falling, viscous dissipation is lower and accretion can proceed. Over nighttime, the largest temperature depressions occur in the subglacial system, but water flux is lowest and accretion rates are negligible. We conclude by inferring that overdeepened glaciers with only clear water flows evolve toward stronger supercooling regimes rather than toward a dynamic equilibrium. Stabilizing feedbacks are unlikely to occur through glacier hydrology alone, and other processes, such as erosion, sedimentation, and sliding, must play an important role.Hydrologic sciences, Physical geographyttc2119Lamont-Doherty Earth ObservatoryArticlesEvolution of Subglacial Overdeepenings in Response to Sediment Redistribution and Glaciohydraulic Supercoolinghttp://academiccommons.columbia.edu/catalog/ac:164908
Creyts, Timothy T.; Clarke, Garry K. C.; Church, Michaelhttp://hdl.handle.net/10022/AC:P:21531Thu, 05 Sep 2013 00:00:00 +0000Glaciers erode bedrock rapidly, but evacuation of sediments requires efficient subglacial drainage networks. If glaciers erode more rapidly than evacuation proceeds, a protective subglacial till layer can form to armor the bed. Where glaciers cross overdeepenings, local closed depressions, the bed slope opposes the ice surface and lowers the hydraulic potential gradient that drives water flow. Here, we present results of a dynamic, distributed model of coupled basal water flow and sediment transport to show how overdeepenings evolve over the course of a melt season. We use steady-state calculations as well as numerical simulations to understand how alluvial bed erosion alters overdeepenings. Numerical results from a modified form of the Spring-Hutter equations show behaviors that cannot be inferred from either local or steady-state calculations. In general, opposition of surface and bed slopes lessens sediment transport regardless of ice accretion from glaciohydraulic supercooling. Drainage efficiency strongly affects erosion and deposition rates. Results show characteristic behaviors of flow through overdeepenings such as overpressured water systems and accretion rates compatible with field measurements. Simulations that start with overdeepened glacier configurations progress out of a freezing regime where glaciohydraulic supercooling occurs. This progression indicates that glacier hydrology is more strongly affected by erosion and deposition than by freezing from glaciohydraulic supercooling. We discuss how this outcome affects glacier erosion and sediment transport under modern and past ice sheets.Hydrologic sciences, Physical geographyttc2119Lamont-Doherty Earth ObservatoryArticlesA Hydroclimatic Regionalization of Central Mongolia as Inferred from Tree Ringshttp://academiccommons.columbia.edu/catalog/ac:163789
Leland, Caroline; Pederson, Neil; Hessl, Amy; Nachin, Baatarbileg; Davi, Nicole K.; D'Arrigo, Rosanne Dorothy; Jacoby, Gordonhttp://hdl.handle.net/10022/AC:P:21214Sat, 03 Aug 2013 00:00:00 +0000In arid and semi-arid regions of the world, such as Mongolia, the future of water resources under a warming climate is of particular concern. The influence of increasing temperatures on precipitation is difficult to predict because precipitation trends in coming decades could have a high degree of spatial variability. In this study, we applied a rotated principal component analysis (RPCA) to a network of 20 tree-ring chronologies across central Mongolia from 1790 to 1994 to evaluate spatial hydroclimatic variability and to place recent variability in the context of the past several centuries. The RPCA results indicate that the network consists of four tree-growth anomaly regions, which were found to be relatively stable through time and space. Correlation analyses reveal spatial linkages between the tree-growth anomalies and instrumental data, where annual streamflow variability was strongly associated with tree-growth anomalies from their respective regions from 1959 to 1994 (r = 0.52–0.64, p < 0.05). This study highlights the extent of spatial variability in hydroclimate across central Mongolia and emphasizes the value of using tree-ring networks in locations with limited instrumental records.Hydrologic sciences, Climate changenp150, nkd5, rd5, gcj1Lamont-Doherty Earth ObservatoryArticlesTracers of physical and biogeochemical processes, past changes and ongoing anthropogenic impactshttp://academiccommons.columbia.edu/catalog/ac:162601
Grégoire, Marilaure; Anderson, Robert F.; Delille, Bruno; Jeandel, Catherine; Speich, Sabrinahttp://hdl.handle.net/10022/AC:P:20823Thu, 20 Jun 2013 00:00:00 +0000The 43rd International Liege Colloquium on Ocean Dynamics (http://modb.oce.ulg.ac.be/colloquium/) gathered a hundred scientists from around the world to discuss new developments and insights related to tracers and proxies (from temperature and salinity to gases and isotopes) with a particular attention on the use of Trace Elements and Isotopes (TEI) as tracers. The colloquium was organized in connection with the Geotraces program (an ongoing international study of the global marine biogeochemical cycles of trace elements and their isotopes, http://www.geotraces.org/) and was the occasion to present the wealth of data collected during large oceanographic expeditions that occurred in connection with the International Polar year. In this framework, particular emphasis was given to the BONUS-GoodHope project, a multi-disciplinary oceanographic cruise that coupled full-depth ocean and atmosphere physical and biogeochemical observations, including trace metals and isotopes (Speich et al. 2013; Speich et al. 2008). The special issue presents a collection of papers dealing with these different thematics.Biogeochemistry, Chemical oceanography, Hydrologic sciencesrfa1Lamont-Doherty Earth ObservatoryArticlesDynamical Structure of Extreme Floods in the U.S. Midwest and the United Kingdomhttp://academiccommons.columbia.edu/catalog/ac:159618
Nakamura, Jennifer A.; Lall, Upmanu; Kushnir, Yochanan; Robertson, Andrew W.; Seager, Richardhttp://hdl.handle.net/10022/AC:P:19871Tue, 23 Apr 2013 00:00:00 +0000Twenty extreme spring floods that occurred in the Ohio basin between 1901 and 2008, identified from daily river discharge data, are investigated and compared to the April 2011 Ohio River flood event. Composites of synoptic fields for the flood events show that all of these floods are associated with a similar pattern of sustained advection of low-level moisture and warm air from the tropical Atlantic Ocean and the Gulf of Mexico. The typical flow conditions are governed by an anomalous semistationary ridge, situated east of the U.S. East Coast, that steers the moisture and converges it into the Ohio River valley. Significantly, the moisture path common to all of the 20 cases studied here as well as the case of April 2011 is distinctly different from the normal path of Atlantic moisture during spring, which occurs farther west. It is shown further that the Ohio basin moisture convergence responsible for the floods is caused primarily by the atmospheric circulation anomaly advecting the climatological mean moisture field. Transport and related convergence due to the covariance between moisture anomalies and circulation anomalies are of secondary but nonnegligible importance. The importance of atmospheric circulation anomalies to floods is confirmed by conducting a similar analysis for a series of winter floods on the river Eden in northwest England.Hydrologic sciences, Atmospheric sciences, Meteorologyjam148, ula2, yk16, awr2001, rs229Lamont-Doherty Earth Observatory, International Research Institute for Climate and Society, Earth and Environmental EngineeringArticlesHave Aerosols Caused the Observed Atlantic Multidecadal Variability?http://academiccommons.columbia.edu/catalog/ac:159154
Ting, Mingfang; Delworth, Thomas L.; Zhang, Rong; Kushnir, Yochanan; Sutton, Rowan; Hodson, Daniel L. R.; Dixon, Keith W.; Held, Isaac M.; Marshall, John; Msadek, Rym; Ming, Yi; Robson, Jon; Rosati, Anthonoy J.; Vecchi, Gabriel A.http://hdl.handle.net/10022/AC:P:19750Fri, 12 Apr 2013 00:00:00 +0000Identifying the prime drivers of the twentieth-century multidecadal variability in the Atlantic Ocean is crucial for predicting how the Atlantic will evolve in the coming decades and the resulting broad impacts on weather and precipitation patterns around the globe. Recently, Booth et al. showed that the Hadley Centre Global Environmental Model, version 2, Earth system configuration (HadGEM2-ES) closely reproduces the observed multidecadal variations of area-averaged North Atlantic sea surface temperature in the twentieth century. The multidecadal variations simulated in HadGEM2-ES are primarily driven by aerosol indirect effects that modify net surface shortwave radiation. On the basis of these results, Booth et al. concluded that aerosols are a prime driver of twentieth-century North Atlantic climate variability. However, here it is shown that there are major discrepancies between the HadGEM2-ES simulations and observations in the North Atlantic upper-ocean heat content, in the spatial pattern of multidecadal SST changes within and outside the North Atlantic, and in the subpolar North Atlantic sea surface salinity. These discrepancies may be strongly influenced by, and indeed in large part caused by, aerosol effects. It is also shown that the aerosol effects simulated in HadGEM2-ES cannot account for the observed anticorrelation between detrended multidecadal surface and subsurface temperature variations in the tropical North Atlantic. These discrepancies cast considerable doubt on the claim that aerosol forcing drives the bulk of this multidecadal variability.Atmospheric sciences, Hydrologic sciencesmt2204, yk16Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesInterocean Exchangehttp://academiccommons.columbia.edu/catalog/ac:158992
Gordon, Arnold L.http://hdl.handle.net/10022/AC:P:19711Wed, 10 Apr 2013 00:00:00 +0000Earth’s climate, responding to the different thermodynamic properties of the land and ocean surfaces, is sensitive to the continental configuration and distribution of mountain ranges. This is clearly seen in the pattern of mean annual and seasonal range in such climate parameters as temperature and humidity and in the quasistationary patterns of atmospheric circulation, from small-scale sea breezes to planetary waves.Physical oceanography, Hydrologic sciences, Atmospheric sciencesalg3Lamont-Doherty Earth Observatory, Earth and Environmental SciencesBook chaptersFive centuries of Upper Indus River flow from tree ringshttp://academiccommons.columbia.edu/catalog/ac:158923
Cook, Edward R.; Palmer, Jonathan G.; Ahmed, Moinuddin; Woodhouse, Connie A.; Fenwick, Pavla; Zafar, Muhammad Usama; Wahab, Muhammad; Khan, Nasrullahhttp://hdl.handle.net/10022/AC:P:19694Mon, 08 Apr 2013 00:00:00 +0000Water wars are a prospect in coming years as nations struggle with the effects of climate change, growing water demand, and declining resources. The Indus River supplies water to the world’s largest contiguous irrigation system generating 90% of the food production in Pakistan as well as 13 gigawatts of hydroelectricity. Because any gap between water supply and demand has major and far-reaching ramifications, an understanding of natural flow variability is vital – especially when only 47 years of instrumental record is available. A network of tree-ring sites from the Upper Indus Basin (UIB) was used to reconstruct river discharge levels covering the period AD 1452–2008. Novel methods tree-ring detrending based on the ‘signal free’ method and estimation of reconstruction uncertainty based on the ‘maximum entropy bootstrap’ are used. This 557-year record displays strong inter-decadal fluctuations that could not have been deduced from the short gauged record. Recent discharge levels are high but not statistically unprecedented and are likely to be associated with increased meltwater from unusually heavy prior winter snowfall. A period of prolonged below-average discharge is indicated during AD 1572–1683. This unprecedented low-flow period may have been a time of persistently below-average winter snowfall and provides a warning for future water resource planning. Our reconstruction thus helps fill the hydrological information vacuum for modeling the Hindu Kush–Karakoram–Himalayan region and is useful for planning future development of UIB water resources in an effort to close Pakistan’s “water gap”. Finally, the river discharge reconstruction provides the basis for comparing past, present, and future hydrologic changes, which will be crucial for detection and attribution of hydroclimate change in the Upper Indus Basin.Climate change, Water resources management, Hydrologic scienceserc1Lamont-Doherty Earth ObservatoryArticlesGround and Satellite Observations (2005-2011): Senator Beck Basin, Southwestern Coloradohttp://academiccommons.columbia.edu/catalog/ac:158754
Naud, Catherine M.http://hdl.handle.net/10022/AC:P:19566Mon, 01 Apr 2013 00:00:00 +0000The Center for Snow and Avalanche Studies (CSAS; www.snowstudies.org) provides ground-based observations of temperature, relative humidity, snowpack depth, and longwave downward flux in the San Juan Mountains, at the Senator Beck Study Plot (37.9°N - 107.725°W at 3719 m, in alpine tundra) and Swamp Angel Study Plot (37.9°N - 107.711°W at 3368 m, in a sub-alpine meadow). The longwave fluxes are measured with a Kipp and Zonen model CG4 pyrgeometer, which has a 180º field of view. The CG4 is designed to minimize the effects of window heating in direct sunlight, during daylight measurements. The air temperature and relative humidity are measured with a Campbell-Vaisala model CS500-U Humitter®. All measurements are obtained every 5 seconds and available as hourly averages during the period 2005-2010.The data are archived and described on: http://www.snowstudies.org/ Here we compiled the data into single ncdf files per site for the entire period of operation. In addition, we collected NASA-MODIS cloud product observations (MOD06 and MYD06) files, namely cloud fraction and cloud optical thickness and created a new file for the Senator Beck study plot, where coincident ground and satellite observations are selected. This new dataset is a subset of the ground observations only files. 1. Hourly Ground Based Data From Two Plots: Senator Beck and Swamp Angel Study Plots These are hourly observations from the two plots between 2005-2011. In addition, a few other variables were estimated. These include: specific humidity (based on relative humidity, temperature and pressure), upward longwave radiation (based on soil surface temperature), surface pressure for Senator Beck plot (from surface pressure at Swamp Angel plot), and cloud mask (based on solar radiation). Please see the "Readme" file provided for each data file for a detail description of the data content. 2. Ground and Satellite Data: Senator Beck Plot only This data include only the coincident hourly observations from ground and satellite (MODIS) at the Senator Beck site. Therefore, there are generally two observations per day. Day and night flag is also assigned to the data. The satellite observations included here are: (1) cloud fraction and (2) cloud optical depth (during overcast conditions only).Atmospheric sciences, Meteorology, Hydrologic sciencescn2140Applied Physics and Applied MathematicsDatasetsTropical Intraseasonal Variability in Version 3 of the GFDL Atmosphere Modelhttp://academiccommons.columbia.edu/catalog/ac:157013
Benedict, James J.; Maloney, Eric D.; Sobel, Adam H.; Frierson, Dargan M.; Donner, Leo J.http://hdl.handle.net/10022/AC:P:19147Thu, 21 Feb 2013 00:00:00 +0000Tropical intraseasonal variability is examined in version 3 of the Geophysical Fluid Dynamics Laboratory Atmosphere Model (AM3). In contrast to its predecessor AM2, AM3 uses a new treatment of deep and shallow cumulus convection and mesoscale clouds. The AM3 cumulus parameterization is a mass-flux-based scheme but also, unlike that in AM2, incorporates subgrid-scale vertical velocities; these play a key role in cumulus microphysical processes. The AM3 convection scheme allows multiphase water substance produced in deep cumuli to be transported directly into mesoscale clouds, which strongly influence large-scale moisture and radiation fields. The authors examine four AM3 simulations using a control model and three versions with different modifications to the deep convection scheme. In the control AM3, using a convective closure based on CAPE relaxation, both MJO and Kelvin waves are weak relative to those in observations. By modifying the convective closure and trigger assumptions to inhibit deep cumuli, AM3 produces reasonable intraseasonal variability but a degraded mean state. MJO-like disturbances in the modified AM3 propagate eastward at roughly the observed speed in the Indian Ocean but up to 2 times the observed speed in the west Pacific Ocean. Distinct differences in intraseasonal convective organization and propagation exist among the modified AM3 versions. Differences in vertical diabatic heating profiles associated with the MJO are also found. The two AM3 versions with the strongest intraseasonal signals have a more prominent “bottom heavy” heating profile leading the disturbance center and “top heavy” heating profile following the disturbance. The more realistic heating structures are associated with an improved depiction of moisture convergence and intraseasonal convective organization in AM3.Atmospheric sciences, Hydrologic sciencesahs129Applied Physics and Applied Mathematics, Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesNorth Atlantic influence on 19th–20th century rainfall in the Dead Sea watershed, teleconnections with the Sahel, and implication for Holocene climate fluctuationshttp://academiccommons.columbia.edu/catalog/ac:153712
Kushnir, Yochanan; Stein, Mordechaihttp://hdl.handle.net/10022/AC:P:15033Mon, 22 Oct 2012 00:00:00 +0000The importance of understanding processes that govern the hydroclimate of the Mediterranean Basin is highlighted by the projected significant drying of the region in response to the increase in greenhouse gas concentrations. Here we study the long-term hydroclimatic variability of the central Levant region, situated in the eastern boundary of the Basin, as reveled by instrumental observations and the Holocene record of Dead Sea level variations. Observations of 19th and 20th century precipitation in the Dead Sea watershed region display a multidecadal, anti-phase relationship to North Atlantic (NAtl) sea surface temperature (SST) variability, such that when the NAtl is relatively cold, Jerusalem experiences higher than normal precipitation and vice versa. This association is underlined by a negative correlation to precipitation in the sub-Saharan Sahel and a positive correlation to precipitation in western North America, areas that are also affected by multidecadal NAtl SST variability. These observations are consistent with a broad range of Holocene hydroclimatic fluctuations from the epochal, to the millennial and centennial time scales, as displayed by the Dead Sea lake level, by lake levels in the Sahel, and by direct and indirect proxy indicators of NAtl SSTs. On the epochal time scale, the gradual cooling of NAtl SSTs throughout the Holocene in response to precession-driven reduction of summer insolation is associated with previously well-studied wet-to-dry transition in the Sahel and with a general increase in Dead Sea lake levels from low stands after the Younger Dryas to higher stands in the mid- to late-Holocene. On the millennial and centennial time scales there is also evidence for an anti-phase relationship between Holocene variations in the Dead Sea and Sahelian lake levels and with proxy indicators of NAtl SSTs. However the records are punctuated by abrupt lake-level drops, which appear to be in-phase and which occur during previously documented abrupt major cooling events in the Northern Hemisphere. We propose that the mechanisms by which NAtl SSTs affect precipitation in the central Levant is related to the tendency for high (low) pressure anomalies to persist over the eastern North Atlantic/Western Mediterranean region when the Basin is cold (warm). This, in turn, affects the likelihood of cold air outbreaks and cyclogenesis in the Eastern Mediterranean and, consequently, rainfall in the central Levant region. Depending on its phase, this natural mechanism can alleviate or exacerbate the anthropogenic impact on the regions' hydroclimatic future.Hydrologic sciencesyk16, ms3670Lamont-Doherty Earth ObservatoryArticlesAutocalibration of HSPF for Simulation of Streamflow Using a Genetic Algorithmhttp://academiccommons.columbia.edu/catalog/ac:152232
Sahoo, Debabrata; Smith, Patricia; Ines, Amor Valeriano M.http://hdl.handle.net/10022/AC:P:14592Tue, 04 Sep 2012 00:00:00 +0000Hydrologic models are essential to watershed planning and management, particularly in the San Antonio River watershed where competition for scarce water resources is a challenge. As a result, the calibration and validation of hydrologic models are essential steps for their successful application. In this study, we examined the use of a loosely coupled genetic algorithm (GA) as an autocalibration tool for optimization of model parameters for the Hydrologic Simulation Program - Fortran (HSPF), a model frequently used in surface hydrology and water quality modeling. The GA-HSPF model is a more objective and less time-consuming alternative to traditional trial-and-error methods. The objective function was optimized by minimizing the mean absolute error (MAE) between corresponding simulated and observed average daily streamflow in the San Antonio River watershed. The MAE was used to evaluate the fitness of the parameter set in the GA. The calibrated model parameters (LZSN, INFILT, AGWRC, UZSN, DEEPFR, LZETP, and INTFW) were selected based on a sensitivity analysis from a previous study. Goodness-of-fit of the GA calibrated model was evaluated using the Nash-Sutcliffe coefficient of efficiency, MAE, root mean square error, flow duration curves, wavelet analysis, and total volume error. Overall simulation time with 2000 model simulations was 11 days, which can be improved significantly under parallel computing, as GA-HSPF simulations are highly independent. The objective function ceased improvement after approximately 250 simulations, with a minimized MAE of 25.8 m3/s. With the exception of DEEPFR, all optimized model parameter values were within the range cited in the literature. Nash-Sutcliffe coefficients in all simulations were above 0.5, suggesting that the simulated flows were in good agreement with the observed flows. Visual comparison between observed and simulated stream flow using time series and flow duration curves showed that the GA calibrated model was unable to simulate peak flow events accurately, particularly in the 0% to 10% exceedence range. It is hypothesized that the storage-based routing scheme in HSPF limits its ability to predict peak flows in this watershed. Comparison between observed and simulated flows in the wavelet domain indicated that the GA calibrated model was not able to preserve the scale and location of some high frequencies, but the scale and location of lower frequencies were preserved. The cyclic nature of the streamflow in this watershed was more prominent in lower frequencies. While overall flow rates were adequately predicted using a GA-HSPF approach, future work in this watershed needs to focus on multi-objective optimization that optimizes both volumes and peak flows. The GA-HSPF model offers an objective and efficient method for calibration and validation, a useful tool in watershed planning efforts.Hydrologic sciencesavi2101International Research Institute for Climate and SocietyArticlesThree centuries of shifting hydroclimatic regimes across the Mongolian Breadbaskethttp://academiccommons.columbia.edu/catalog/ac:151662
Pederson, Neil; Leland, Caroline; Nachin, B.; Hessl, A. E.; Bell, A. R.; Martin Benito, Dario; Saladyga, T.; Suran, B.; Brown, P. M.; Davi, Nicole K.http://hdl.handle.net/10022/AC:P:14390Wed, 15 Aug 2012 00:00:00 +0000In its continuing move toward resource independence, Mongolia has recently entered a new agricultural era. Large crop fields and center-pivot irrigation have been established in the last 10 years across Mongolia's "Breadbasket": the Bulgan, Selenge and Tov aimags of northcentral Mongolia. Since meteorological records are typically short and spatially diffuse, little is known about the frequency and scale of past droughts in this region. We use six chronologies from the eastern portion of the breadbasket region to reconstruct streamflow of the Yeruu River. These chronologies accounted for 60.8% of May–September streamflow from 1959 to 1987 and 74.1% from 1988 to 2001. All split, calibration-verification statistics were positive, indicating significant model reconstruction. Reconstructed Yeruu River streamflow indicates the 20th century to be wetter than the two prior centuries. When comparing the new reconstruction to an earlier reconstruction of Selenge River streamflow, representing the western portion of the breadbasket region, both records document more pluvial events of greater intensity during 20th century versus prior centuries and indicate that the recent decade of drought that lead to greater aridity across the landscape is not unusual in the context of the last 300 years. Most interestingly, variability analyses indicate that the larger river basin in the western breadbasket (the Selenge basin) experiences greater swings in hydroclimate at multi-decadal to centennial time scales while the smaller basin in the eastern portion of the breadbasket (the Yeruu basin) is more stable. From this comparison, there would be less risk in agricultural productivity in the eastern breadbasket region, although the western breadbasket region can potentially be enormously productive for decades at a time before becoming quite dry for an equally long period of time. These results indicate that farmers and water managers need to prepare for both pluvial conditions like those in the late-1700s, and drier conditions like those during the early and mid-1800s. Recent studies have indicated that cultures with plentiful resources are more vulnerable when these resources become diminished. Thus, the instrumental records of the 20th century should not be used as a model of moisture availability. Most importantly, the geographic mismatch between precipitation, infrastructure, and water demand could turn out to be particularly acute for countries like Mongolia, especially as these patterns can switch in space through time.Hydrologic sciences, Agriculturenp150, dm2833, nkd5Lamont-Doherty Earth ObservatoryArticlesNear-Surface Soil Moisture Assimilation for Quantifying Effective Soil Hydraulic Properties under Different Hydroclimatic Conditionshttp://academiccommons.columbia.edu/catalog/ac:150506
Ines, Amor Valeriano M.; Mohanty, Binayak P.http://hdl.handle.net/10022/AC:P:14204Mon, 23 Jul 2012 00:00:00 +0000We conducted a validation study of a newly developed near-surface soil moisture assimilation scheme for estimating effective soil hydraulic properties using soil moisture data from different hydroclimatic regions, including semihumid Oklahoma, humid Iowa and Illinois, and temperate humid China. A genetic algorithm (GA) was used to estimate the effective soil water retention θ(h) and hydraulic conductivity K(h) functions of an effective modeling domain by minimizing errors between observed near-surface soil moisture and values simulated with the Richards-based Soil–Water–Atmosphere–Plant (SWAP) model. The parameter estimation approach considered uncertainties in the initial and bottom boundary conditions, rooting depth, and root density by creating simulation ensembles based on combinations of several modeling conditions and a multipopulation approach in the GA to estimate uncertainties in the derived soil hydraulic properties. The results showed that θ(h) is not very sensitive to variations in the initial and boundary conditions, rooting depth, and root density applied on the modeling domain. The value of K(h) was found to be more sensitive to variations in rooting depth and root density than to variations in the initial and boundary conditions. With the modeling domain better represented, the estimated θ(h) and K(h) functions were found to be satisfactory in most of the locations studied. They were validated using laboratory-measured θ(h) and K sat, observed soil moisture in the field, and soil hydraulic properties from the UNSODA database. Our study indicates, however, that the homogeneous-medium assumption commonly used to effectively describe a heterogeneous system may fail to closely represent a highly heterogeneous (layered) soil profile if only the near-surface soil moisture data are used to define the subsurface soil hydraulic properties. Additional soil moisture data from deeper depths may be needed to better estimate the effective soil hydraulic properties of highly heterogeneous systems.Hydrologic sciencesavi2101International Research Institute for Climate and SocietyArticlesSoil hydraulic properties in one-dimensional layered soil profile using layer-specific soil moisture assimilation schemehttp://academiccommons.columbia.edu/catalog/ac:150494
Shin, Yongchul; Mohanty, Binayak P.; Ines, Amor Valeriano M.http://hdl.handle.net/10022/AC:P:14202Mon, 23 Jul 2012 00:00:00 +0000We developed a layer-specific soil-moisture assimilation scheme using a simulation-optimization framework, Soil-Water-Atmosphere-Plant model with genetic algorithm (SWAP-GA). Here, we explored the quantification of the soil hydraulic properties in a layered soil column under various combinations of soil types, vegetation covers, bottom boundary conditions and soil layering using idealized (synthetic) numerical studies and actual field experiments. We demonstrated that soil layers and vertical heterogeneity (layering arrangements) could impact to the uncertainty of quantifying soil hydraulic parameters. We also found that, under layered soil system, when the subsurface flows are dominated by upward fluxes, e.g., from a shallow water table, the solution to the inverse problem appears to be more elusive. However, when the soil profile is predominantly draining, the soil hydraulic parameters could be fairly estimated well across soil layers, corroborating the results of past studies on homogenous soil columns. In the field experiments, the layer-specific assimilation scheme successfully matched soil moisture estimates with observations at the individual soil layers suggesting that this approach could be applied in real world conditions.Hydrologic sciencesavi2101International Research Institute for Climate and SocietyArticlesInverse Modeling to Quantify Irrigation System Characteristics and Operational Managementhttp://academiccommons.columbia.edu/catalog/ac:150501
Ines, Amor Valeriano M.; Droogers, Peterhttp://hdl.handle.net/10022/AC:P:14203Mon, 23 Jul 2012 00:00:00 +0000Remotely sensed (RS) data is a major source to obtain spatial data required for hydrological models. The challenge for the future is to obtain besides the more direct observable data (landcover, leaf area index, digital elevation model and evapotranspiration), non-visible data such as soil characteristics, groundwater depth and irrigation practices.In this study we have explore the option of using inverse modeling to obtain these non-RS-visible data. For a command area in Haryana, India, we applied for the 2000–2001 rabi season a RS-GIS-combined inverse modeling approach to derive non-RS-visible data required in the regional application of hydrological models. A Genetic Algorithm loaded stochastic physically based soil-water-atmosphere-plant model (SWAP) was developed for the inverse problem and used in the study. The results showed good agreement with the inventoried data such as soil hydraulic properties, sowing dates, ground water depths, irrigation practices and water quality. The derived data could be used to predict the state of the system at anytime in the cropping season, which can be used to evaluate operational management strategies.Hydrologic sciences, Remote sensingavi2101International Research Institute for Climate and SocietyArticlesBias correction of daily GCM rainfall for crop simulation studieshttp://academiccommons.columbia.edu/catalog/ac:150515
Ines, Amor Valeriano M.; Hansen, James W.http://hdl.handle.net/10022/AC:P:14205Mon, 23 Jul 2012 00:00:00 +0000General circulation models (GCMs), used to predict rainfall at a seasonal lead-time, tend to simulate too many rainfall events of too low intensity relative to individual stations within a GCM grid cell. Even if bias in total rainfall is corrected relative to a target location, this distortion of frequency and intensity is expected to adversely affect simulations of crop growth and yield. We present a procedure that calibrates both the frequency and the intensity distribution of daily GCM rainfall relative to a target station, and demonstrate its application to maize yield simulation at a location in semi-arid Kenya. If GCM rainfall frequency is greater than observed frequency for a given month, averaged across years, GCM rainfall frequency is corrected by discarding rainfall events below a calibrated threshold. To correct the intensity distribution, each GCM rainfall amount above the calibrated threshold is mapped from the GCM intensity distribution onto the observed distribution. We used a gamma distribution for observed rainfall intensity, and considered both gamma and empirical distributions for GCM rainfall intensity. At the study location, the proposed correction procedure corrected both the mean and variance of monthly and seasonal GCM rainfall total, frequency and mean intensity. The empirical (GCM)-gamma (observed) transformation overestimated mean intensity slightly. A simple multiplicative shift did a better job of correcting monthly and seasonal rainfall totals, but left substantial frequency and intensity bias. All of the bias correction procedures improved maize yield simulations, but resulted in substantial negative mean bias. This bias appears to be associated with a tendency for the GCM rainfall to be more strongly autocorrelated than observed rainfall, resulting in unrealistically long dry spells during the growing season. Nonlinearity of crop response to the variability of water availability across GCM realizations may also contribute. Averaging simulated yields each year across multiple GCM realizations improved yield predictions. The proposed correction procedure provides an option for using the daily output of dynamic climate prediction models for impact studies in a manner that preserves any useful predictive information about the timing of rainfall within the season. However, its practical utility for yield forecasting at a long lead-time may be limited by the ability of GCMs to simulate rainfall with a realistic time structure.Hydrologic sciencesavi2101, jwh85International Research Institute for Climate and SocietyArticlesThree centuries of Myanmar monsoon climate variability inferred from teak tree ringshttp://academiccommons.columbia.edu/catalog/ac:144830
D'Arrigo, Rosanne Dorothy; Palmer, Jonathan; Ummenhofer, Caroline C.; Kyaw, Nyi Nyi; Krusic, PaulMon, 20 Feb 2012 00:00:00 +0000Asian monsoon extremes critically impact much of the globe's population. Key gaps in our understanding of monsoon climate remain due to sparse coverage of paleoclimatic information, despite intensified recent efforts. Here we describe a ring width chronology of teak, one of the first high-resolution proxy records for the nation of Myanmar. Based on 29 samples from 20 living trees and spanning from 1613-2009, this record, from the Maingtha forest reserve north of Mandalay, helps fill a substantial gap in spatial coverage of paleoclimatic records for monsoon Asia. Teak growth is positively correlated with rainfall and Palmer Drought Severity Index variability over Myanmar, during and prior to the May-September monsoon season (e.g., r = 0.38 with Yangon rainfall, 0.001, n 68). Importantly, this record also correlates significantly with larger-scale climate indices, including core Indian rainfall (23°N, 76°E; a particularly sensitive index of the monsoon), and the El Niño-Southern Oscillation (ENSO). The teak ring width value following the so-called 1997-98 El Niño of the Century suggests that this was one of the most severe droughts in the past ~300 years in Myanmar. Evidence for past dry conditions inferred for Myanmar is consistent with tree-ring records of decadal megadroughts developed for Thailand and Vietnam. These results confirm the climate signature related to monsoon rainfall in the Myanmar teak record and the considerable potential for future development of climate-sensitive chronologies from Myanmar and the broader region of monsoon Asia.Paleoclimate science, Climate change, Hydrologic sciencesrd5Lamont-Doherty Earth ObservatoryArticlesSoil moisture estimation from inverse modeling using multiple criteria functionshttp://academiccommons.columbia.edu/catalog/ac:144142
Charoenhirunyingyos, Sujittra; Honda, Kiyoshi; Kamthonkiat, Daroonwan; Ines, Amor Valeriano M.http://hdl.handle.net/10022/AC:P:12471Tue, 07 Feb 2012 00:00:00 +0000Soil hydraulic parameters are essential inputs to agricultural and hydrologic models for simulating soil moisture. These parameters however are difficult to obtain especially when the application is aimed at the regional scale. Laboratory and field methods have been used for quantifying soil hydraulic parameters but they are proved to be laborious and expensive. An emerging alternative of estimating soil hydraulic parameters is soil moisture model inversion using remote sensing (RS) data. Although soil hydraulic parameters could not be derived directly from remote sensing, they could be quantified by the inverse modeling of RS data. In this study, we conducted a multi-criteria inverse modeling approach to estimate the rootzone soil hydraulic parameters in a rainfed rice field at depths 3, 12, 28 and 60 cm, respectively. The conditioning data used in the inverse modeling are leaf area index (LAI) and actual evapotranspiration (ETa) from satellite imageries, and soil moisture (SM) data from in situ measurements. The performances of all the model inversion experiments were evaluated against observed soil moisture in the field, and measured LAI during the growing season. The results showed that using remotely sensed LAI and ETa in the inverse modeling provided a good matching between observed and simulated soil moisture down to 28 cm depth from the soil surface. With the addition of soil moisture information from the site, the model inversion significantly improved the soil moisture simulation up to a depth of 60 cm.Hydrologic sciences, Remote sensingavi2101International Research Institute for Climate and SocietyArticlesSoil hydraulic parameters estimated from satellite information through data assimilationhttp://academiccommons.columbia.edu/catalog/ac:144148
Charoenhirunyingyos, Sujittra; Honda, Kiyoshi; Kamthonkiat, Daroonwan; Ines, Amor Valeriano M.http://hdl.handle.net/10022/AC:P:12473Tue, 07 Feb 2012 00:00:00 +0000Leaf area index (LAI) and actual evapotranspiration (ETa) from satellite observations were used to estimate simultaneously the soil hydraulic parameters of four soil layers down to 60 cm depth using the combined soil water atmosphere plant and genetic algorithm (SWAPâ€“GA) model. This inverse model assimilates the remotely sensed LAI and/or ETa by searching for the most appropriate sets of soil hydraulic parameters that could minimize the difference between the observed and simulated LAI (LAIsim) or simulated ETa (ETasim). The simulated soil moisture estimates derived from soil hydraulic parameters were validated using values obtained from soil moisture sensors installed in the field. Results showed that the soil hydraulic parameters derived from LAI alone yielded good estimations of soil moisture at 3 cm depth; LAI and ETa in combination at 12 cm depth, and ETa alone at 28 cm depth. There appeared to be no match with measurement at 60 cm depth. Additional information would therefore be needed to better estimate soil hydraulic parameters at greater depths. Despite this inability of satellite data alone to provide reliable estimates of soil moisture at the lowest depth, derivation of soil hydraulic parameters using remote sensing methods remains a promising area for research with significant application potential. This is especially the case in areas of water management for agriculture and in forecasting of floods or drought on the regional scale.Hydrologic sciences, Remote sensingavi2101International Research Institute for Climate and SocietyArticlesDecoupling of As and Fe release to Bangladesh groundwater under reducing conditions. Part I: Evidence from sediment profileshttp://academiccommons.columbia.edu/catalog/ac:143266
Horneman, Allan H.; Geen, Alexander van; Kent, Dennis V.; Mathe, P. E.; Zheng, Yan; Dhar, R. K.; O'Connell, Suzanne B.; Hoque, M. A.; Aziz, Zahid; Shamsudduha, M.; Seddique, A. A.; Ahmed, K. M.http://hdl.handle.net/10022/AC:P:12200Fri, 13 Jan 2012 00:00:00 +0000This study reexamines the notion that extensive As mobilization in anoxic groundwater of Bangladesh is intimately linked to the dissolution of Fe oxyhydroxides on the basis of analyses performed on a suite of freshly collected samples of aquifer material. Detailed sediment profiles extending to 40 to 70 m depth below the surface were obtained at six sites where local groundwater As concentrations were known to span a wide range. The sediment properties that were measured include (1) the proportion of Fe(II) in the Fe fraction leached in hot 1.2 N HCl, (2) diffuse spectral reflectance, and (3) magnetic susceptibility. In parallel with local concentrations of dissolved As ranging from <5 to 600 μg/L, Fe(II)/Fe ratios in shallow (gray) Holocene sands tended to gradually increase with depth from values of 0.3 to 0.5 to up to 0.9. In deeper (orange) aquifers of presumed Pleistocene age that were separated from shallow sands by a clay layer and contained <5 μg/L dissolved As, leachable Fe(II)/Fe ratios averaged ∼0.2. There was no consistent relation between sediment Fe(II)/Fe and dissolved Fe concentrations in groundwater in nearby wells. The reflectance measurements indicate a systematic linear relation (R2 of 0.66; n = 151) between the first derivative transform of the reflectance at 520 nm and Fe(II)/Fe. The magnetic susceptibility of the shallow aquifer sands ranged from 200 to 3600 (x 10−9 m3/kg SI) and was linearly related (R2 of 0.75; n = 29) to the concentrations of minerals that could be magnetically separated (0.03 to 0.79% dry weight). No systematic depth trends in magnetic susceptibility were observed within the shallow sands, although the susceptibility of deeper low-As aquifers was low (up to ∼200 × 10−9 m3/kg SI). This set of observations, complemented by incubation results described in a companion paper by van Geen et al. (this volume), suggests that the release of As is linked to the transformation of predominantly Fe (III) oxyhydroxide coatings on sand particles to Fe(II) or mixed Fe(II/III) solid phases with a flatter reflectance spectrum such as siderite, vivianite, or magnetite, without necessarily resulting in the release of Fe to groundwater. The very low As/Fe ratio of magnetically separated minerals compared to the As/Fe of bulk acid leachate (2 vs. 40 10−6, respectively) suggests that such a transformation could be accompanied by a significant redistribution of As to a mobilizable phase on the surface of aquifer particles.Geochemistry, Hydrologic sciencesafv2, dvk2, yz13Lamont-Doherty Earth Observatory, Earth and Environmental SciencesArticlesEpochal Changes in ENSO–Streamflow Relationships in Sri Lankahttp://academiccommons.columbia.edu/catalog/ac:138585
Zubair, Lareef M.; Chandimala, Janakihttp://hdl.handle.net/10022/AC:P:11150Tue, 13 Sep 2011 00:00:00 +0000In an effort to use climate predictions for streamflow and malaria hazard prediction, the decadal variability of the El Niño–Southern Oscillation (ENSO) influence on streamflow and rainfall in the Kelani River in Sri Lanka was investigated based on records from 1925 to 1995. In the last half century, the warm ENSO phase was associated with decreased annual streamflow and the cold ENSO phase with increased streamflow. The annual streamflow had a negative correlation (warm ENSO associated with low streamflow) with the concurrent ENSO index of Niño-3.4 that was significant at the 5% level. This negative correlation with Niño-3.4 is enhanced to a 1% significance level if the aggregate streamflow from January to September alone is considered. There has been a transition in correlation between January–September streamflow and ENSO between the 1950s and 1970s from near or above zero to negative values that have 95% significance levels reminiscent of an epochal shift. This shift was evident when considering the period when the southwest monsoon dominates (April–September) or when correlations were undertaken between the seasonal streamflow and rainfall and the ENSO index in the month prior to each season. Since the relationship between ENSO and Sri Lankan streamflow has strengthened in recent decades the potential for ENSO-based prediction is retained. The epochal shift may also explain why malaria epidemics ceased to co-occur frequently with El Niño episodes after 1945.Hydrologic scienceslz144International Research Institute for Climate and SocietyArticlesPredictability of stream flow and rainfall based on ENSO for water resources management in Sri Lankahttp://academiccommons.columbia.edu/catalog/ac:138582
Chandimala, Janaki; Zubair, Lareef M.http://hdl.handle.net/10022/AC:P:11149Tue, 13 Sep 2011 00:00:00 +0000We investigate the viability of using El Niño–Southern Oscillation (ENSO) and sea surface temperature (SST) data to predict seasonal streamflow for one of the major rivers in Sri Lanka, the Kelani, using correlation analysis, contingency tables, and principal component analysis. The agricultural seasons in Sri Lanka are Yala (April–September) and Maha (October–March). The correlation between the Kelani River streamflow during Yala and ENSO indices (r = −0.41) is significant at 99% level. In addition, the Kelani streamflow during Yala has a correlation with the Central Indian Ocean SST (r = −0.40) that is also significant at the 99% level. The first principal component of the Indo-Pacific Ocean SST is reminiscent of the SST associated with the ENSO mode. A prediction scheme based on this mode for the streamflow during Yala has a skill characterized by a correlation of 0.5 in a cross-validated mode. The prediction of streamflow during Maha is best carried out separately for the two halves of the season. During the El Niño phase, the rainfall during Maha is enhanced during the first half of the season (October–December) and diminished in the second half (January–February). Rainfall rather than streamflow has a better relationship with ENSO from October to December. During the second half of the Maha season, rainfall declines with both warm and cold ENSO phases and any prediction scheme has to take into account this non-linear relationship. Overall, useful skill for seasonal streamflow predictions has been demonstrated for the Yala season and skill for seasonal rainfall predictions for the first and second half of the Maha season has been elucidated.Hydrologic scienceslz144International Research Institute for Climate and SocietyArticlesFinescale Evaluation of Drought in a Tropical Setting: Case Study in Sri Lankahttp://academiccommons.columbia.edu/catalog/ac:138575
Lyon, Bradfield; Zubair, Lareef M.; Ralapanawe, Vidhura; Yahiya, Zeenashttp://hdl.handle.net/10022/AC:P:11147Tue, 13 Sep 2011 00:00:00 +0000In regions of climatic heterogeneity, finescale assessment of drought risk is needed for policy making and drought management, mitigation, and adaptation. The relationship between drought relief payments (a proxy for drought risk) and meteorological drought indicators is examined through a retrospective analysis for Sri Lanka (1960–2000) based on records of district-level drought relief payments and a dense network of 284 rainfall stations. The standardized precipitation index and a percent-of-annual-average index for rainfall accumulated over 3, 6, 9, and 12 months were used, gridded to a spatial resolution of 10 km. An encouraging correspondence was identified between the spatial distribution of meteorological drought occurrence and historical drought relief payments at the district scale. Time series of drought indices averaged roughly over the four main climatic zones of Sri Lanka showed statistically significant (p < 0.01) relationships with the occurrence of drought relief. The 9-month cumulative drought index provided the strongest relationships overall, although 6- and 12-month indicators provided generally similar results. Some cases of appreciable drought without corresponding relief payments could be attributed to fiscal pressures, as during the 1970s. Statistically significant relationships between drought indicators and relief payments point to the potential utility of meteorological drought assessments for disaster risk management. In addition, the study provides an empirical approach to testing which meteorological drought indicators bear a statistically significant relationship to drought relief across a wide range of tropical climates.Hydrologic sciences, Environmental studiesbl225, lz144International Research Institute for Climate and SocietyArticlesThe Strengthening Relationship between ENSO and Northeast Monsoon Rainfall over Sri Lanka and Southern Indiahttp://academiccommons.columbia.edu/catalog/ac:138588
Zubair, Lareef M.; Ropelewski, Chester F.http://hdl.handle.net/10022/AC:P:11151Tue, 13 Sep 2011 00:00:00 +0000Recently, it was reported that the relationship of the Indian southwest monsoon rainfall with El Niño–Southern Oscillation (ENSO) has weakened since around 1980. Here, it is reported that in contrast, the relationship between ENSO and the northeast monsoon (NEM) in south peninsular India and Sri Lanka from October to December has not weakened. The mean circulation associated with ENSO over this region during October to December does not show the weakening evident in the summer and indeed is modestly intensified so as to augment convection. The intensification of the ENSO–NEM rainfall relationship is modest and within the historical record but stands in contrast to the weakening relationship in summer. The intensification of the circulation is consistent with the warming of surface temperatures over the tropical Indian Ocean in recent decades. There is modestly intensified convection over the Indian Ocean, strengthening of the circulation associated with ENSO (Walker circulation), and enhanced rainfall during El Niño episodes in a manner consistent with an augmented ENSO–NEM relationship.Hydrologic scienceslz144, cfr30International Research Institute for Climate and Society, Earth InstituteArticlesThe role of soil moisture initialization in subseasonal and seasonal streamflow prediction: A case study in Sri Lankahttp://academiccommons.columbia.edu/catalog/ac:151133
Mahanama, Sarith P. P.; Koster, Randal D.; Reichle, Rolf H.; Zubair, Lareef M.http://hdl.handle.net/10022/AC:P:11148Tue, 13 Sep 2011 00:00:00 +0000The two main contributors to streamflow predictability at subseasonal to seasonal timescales in tropical regions are: (i) the predictability of meteorologic (particularly precipitation) anomalies, and (ii) the land surface soil moisture state at the start of the forecast period. Meteorological predictions at subseasonal timescale are usually fraught with error and may not be dependable. The accurate initialization of soil moisture, as obtained through real-time land data analysis, may provide skill in subseasonal to seasonal streamflow prediction, even when the prediction skill for rainfall is small. A series of experiments using the Catchment Land Surface Model (CLSM) is performed to characterize the contribution of accurate soil moisture initialization to the skill of streamflow prediction in Sri Lanka at timescales up to 2 months. We find that at the monthly timescale, accurate soil moisture initialization provides between 10% and 60% of the total runoff prediction skill that could be obtained under a perfect prediction of meteorological forcing. Some contributions to streamflow forecast skill are also found for the second month of forecast.Hydrologic scienceslz144International Research Institute for Climate and SocietyArticlesCrop growth and soil water balance modeling to explore water management optionshttp://academiccommons.columbia.edu/catalog/ac:138511
Ines, Amor Valeriano M.; Droogers, Peter; Makin, Ian W.; Das Gupta, Ashimhttp://hdl.handle.net/10022/AC:P:11128Mon, 12 Sep 2011 00:00:00 +0000The study was on the performance of the decision support system for agrotechnology transfer (DSSAT) and the soil water atmosphere plant (SWAP) under an acid sulphate soil. The comparison of these models was done as a prerequisite to the selection of an appropriate model, which is capable of simulating water management scenarios, water balance and crop growth, to be coupled with an adaptive optimization algorithm that can be used to explore water management options.Hydrologic sciences, Agricultureavi2101International Research Institute for Climate and SocietyWorking papersSpatiotemporal analyses of soil moisture from point to footprint scale in two different hydroclimatic regionshttp://academiccommons.columbia.edu/catalog/ac:138437
Joshi, Champa; Mohanty, Binayak P.; Jacobs, Jennifer M.; Ines, Amor Valeriano M.Thu, 08 Sep 2011 00:00:00 +0000This paper presents time stability analyses of soil moisture at different spatial measurement support scales (point scale and airborne remote sensing (RS) footprint scale 800 m × 800 m) in two different hydroclimatic regions. The data used in the analyses consist of in situ and passive microwave remotely sensed soil moisture data from the Southern Great Plains Hydrology Experiments 1997 and 1999 (SGP97 and SGP99) conducted in the Little Washita (LW) watershed, Oklahoma, and the Soil Moisture Experiments 2002 and 2005 (SMEX02 and SMEX05) in the Walnut Creek (WC) watershed, Iowa. Results show that in both the regions soil properties (i.e., percent silt, percent sand, and soil texture) and topography (elevation and slope) are significant physical controls jointly affecting the spatiotemporal evolution and time stability of soil moisture at both point and footprint scales. In Iowa, using point-scale soil moisture measurements, the WC11 field was found to be more time stable (TS) than the WC12 field. The common TS points using data across the 3 year period (2002-2005) were mostly located at moderate to high elevations in both the fields. Furthermore, the soil texture at these locations consists of either loam or clay loam soil. Drainage features and cropping practices also affected the field-scale soil moisture variability in the WC fields. In Oklahoma, the field having a flat topography (LW21) showed the worst TS features compared to the fields having gently rolling topography (LW03 and LW13). The LW13 field (silt loam) exhibited better time stability than the LW03 field (sandy loam) and the LW21 field (silt loam). At the RS footprint scale, in Iowa, the analysis of variance (ANOVA) tests show that the percent clay and percent sand are better able to discern the TS features of the footprints compared to the soil texture. The best soil indicator of soil moisture time stability is the loam soil texture. Furthermore, the hilltops (slope ~0%-0.45%) exhibited the best TS characteristics in Iowa. On the other hand, in Oklahoma, ANOVA results show that the footprints with sandy loam and loam soil texture are better indicators of the time stability phenomena. In terms of the hillslope position, footprints with mild slope (0.93%-1.85%) are the best indicators of TS footprints. Also, at both point and footprint scales in both the regions, land use—land cover type does not influence soil moisture time stability.Hydrologic sciences, Geophysicsavi2101International Research Institute for Climate and SocietyArticlesParameter conditioning with a noisy Monte Carlo genetic algorithm for estimating effective soil hydraulic properties from spacehttp://academiccommons.columbia.edu/catalog/ac:138434
Ines, Amor Valeriano M.; Mohanty, Binayak P.http://hdl.handle.net/10022/AC:P:11112Thu, 08 Sep 2011 00:00:00 +0000The estimation of effective soil hydraulic parameters and their uncertainties is a critical step in all large-scale hydrologic and climatic model applications. Here a scale-dependent (top-down) parameter estimation (inverse modeling) scheme called the noisy Monte Carlo genetic algorithm (NMCGA) was developed and tested for estimating these effective soil hydraulic parameters and their uncertainties. We tested our method using three case studies involving a synthetic pixel (pure and mixed) where all modeling conditions are known, and with actual airborne remote sensing (RS) footprints and a satellite RS footprint. In the synthetic case studies under pure (one soil texture) and mixed-pixel (multiple soil textures) conditions, NMCGA performed well in estimating the effective soil hydraulic parameters even with pixel complexities contributed by various soil types and land management practices (rain-fed/irrigated). With the airborne and satellite remote sensing cases, NMCGA also performed well for estimating effective soil hydraulic properties so that when applied in forward stochastic simulation modeling it can mimic large-scale soil moisture dynamics. The results also suggest a possible scaling down of the effective soil water retention curve (h) at the larger satellite remote sensing pixel compared with the airborne remote sensing pixel. However, it did not generally imply that all effective soil hydraulic parameters should scale down like the soil water retention curve. The reduction of the soil hydraulic parameters was most profound in the saturated soil moisture content ( sat) as we relaxed progressively the soil hydraulic parameter search spaces in our satellite remote sensing studies. Overall, the NMCGA framework was found to be very promising in the inverse modeling of remotely sensed near-surface soil moisture for estimating the effective soil hydraulic parameters and their uncertainties at the remote sensing footprint/climate model grid.Hydrologic sciences, Geophysicsavi2101International Research Institute for Climate and SocietyArticlesNear-surface soil moisture assimilation for quantifying effective soil hydraulic properties using genetic algorithm: 1. Conceptual modelinghttp://academiccommons.columbia.edu/catalog/ac:138431
Ines, Amor Valeriano M.; Mohanty, Binayak P.http://hdl.handle.net/10022/AC:P:11111Thu, 08 Sep 2011 00:00:00 +0000We used a genetic algorithm (GA) to identify soil water retention (h) and hydraulic conductivity K(h) functions by inverting a soil-water-atmosphere-plant (SWAP) model using observed near-surface soil moisture (0-5 cm) as search criterion. Uncertainties of parameter estimates were estimated using multipopulations in GA and considering data and modeling errors. Three hydrologic cases were considered: (1) homogenous free-draining soil column, (2) homogenous soil column with shallow water table, and (3) heterogeneous soil column under free-drainage condition, considering three different rainfall patterns in northern Texas. Results (cases 1 and 2) showed the identifiability of soil hydraulic parameters improving at coarse and fine scales of the soil textural class. Medium-textured soils posed identifiability problems when the soil is dry. Nonlinearity in (h) and K(h) is greater at drier conditions, and some parameters are less sensitive for estimation. Flow regimes controlled by upward fluxes were found less successful, as the information content of observed near-surface data may no longer influence the hydrologic processes in the subsurface. The identifiability of soil hydraulic parameters was found better when the soil profile is predominantly draining. In case 3, top soil layer hydraulic properties were defined using near-surface data alone as criterion. Adding evapotranspiration (ET) improved identification of the second soil layer, although not all parameters were identifiable. Under uncertainties, (h) was found to be well defined while K(h) is more uncertain. Finally, we applied the method to a validation site in Little Washita watershed, Oklahoma, where derived effective soil hydraulic properties closely matched the measured ones at the field site.Hydrologic sciencesavi2101International Research Institute for Climate and SocietyArticlesInverse modelling in estimating soil hydraulic functions: a Genetic Algorithm approachhttp://academiccommons.columbia.edu/catalog/ac:138401
Ines, Amor Valeriano M.; Droogers, Peterhttp://hdl.handle.net/10022/AC:P:11102Thu, 08 Sep 2011 00:00:00 +0000The practical application of simulation models in the field is sometimes hindered by the difficulty of deriving the soil hydraulic properties of the study area. The procedure so-called inverse modelling has been investigated in many studies to address the problem where most of the studies were limited to hypothetical soil profile and soil core samples in the laboratory. Often, the numerical approach called forward-backward simulation is employed to generate synthetic data then added with random errors to mimic the real-world condition. Inverse modelling is used to backtrack the expected values of the parameters. This study explored the potential of a Genetic Algorithm (GA) to estimate inversely the soil hydraulic functions in the unsaturated zone. Lysimeter data from a wheat experiment in India were used in the analysis. Two cases were considered: (1) a numerical case where the forward-backward approach was employed and (2) the experimental case where the real data from the lysimeter experiment were used. Concurrently, the use of soil water, evapotranspiration (ET) and the combination of both were investigated as criteria in the inverse modelling. Results showed that using soil water as a criterion provides more accurate parameter estimates than using ET. However, from a practical point of view, ET is more attractive as it can be obtained with reasonable accuracy on a regional scale from remote sensing observations. The experimental study proved that the forward-backward approach does not take into account the effects of model errors. The formulation of the problem is found to be critical for a successful parameter estimation. The sensitivity of parameters to the objective function and their zone of influence in the soil column are major determinants in the solution. Generally, their effects sometimes lead to non-uniqueness in the solution but to some extent are partly handled by GA. Overall, it was concluded that the GA approach is promising to the inverse problem in the unsaturated zone.Hydrologic sciencesavi2101International Research Institute for Climate and SocietyArticlesNear-surface soil moisture assimilation for quantifying effective soil hydraulic properties using genetic algorithms: 2. Using airborne remote sensing during SGP97 and SMEX02http://academiccommons.columbia.edu/catalog/ac:138114
Ines, Amor Valeriano M.; Mohanty, Binayak P.http://hdl.handle.net/10022/AC:P:11060Thu, 01 Sep 2011 00:00:00 +0000Pixel-based effective soil hydraulic parameters are crucial inputs for large-scale hydroclimatic modeling. In this paper, we extend/apply a genetic algorithm (GA) approach for estimating these parameters at the scale of an airborne remote sensing (RS) footprint. To estimate these parameters, we used a time series of near-surface RS soil moisture data to invert a physically based soil-water-atmosphere-plant (SWAP) model with a (multipopulated) modified-microGA. Uncertainties in the solutions were examined in two ways: (1) by solving the inverse problem under various combinations of modeling conditions in a respective way; and (2) the same as the first method but the inverse solutions were determined in a collective way aimed at finding the robust solutions for all the modeling conditions (ensembles). A cross validation of the derived soil hydraulic parameters was done to check their effectiveness for all the modeling conditions used. For our case studies, we considered three electronically scanned thinned array radiometer (ESTAR) footprints in Oklahoma and four polarimetric scanning radiometer (PSR) footprints in Iowa during the Southern Great Plains 1997 (SGP97) Hydrology Experiment and Soil Moisture Experiment 2002 (SMEX02) campaigns, respectively. The results clearly showed the promising potentials of near-surface RS soil moisture data combined with inverse modeling for determining average soil hydrologic properties at the footprint scale. Our cross validation showed that parameters derived by method 1 under water table (bottom boundary) conditions are applicable also for free-draining conditions. However, parameters derived under free-draining conditions generally produced too wet near-surface soil moisture when applied under water table conditions. Method 2, on the other hand, produced robust parameter sets applicable for all modeling conditions used. These results were validated using distributed in situ soil moisture and soil hydraulic properties measurements, and texture-based data from the UNSODA database. In this study, we conclude that inverse modeling of RS soil moisture data is a promising approach for parameter estimation at large measurement support scale. Nevertheless, the derived effective soil hydraulic parameters are subject to the uncertainties of remotely sensed soil moisture data and from the assumptions used in the soil-water-atmosphere-plant modeling. Method 2 provides a flexible framework for accounting these sources of uncertainties in the inverse estimation of large-scale soil hydraulic properties. We have illustrated this flexibility by combining multiple data sources and various modeling conditions in our large-scale inverse modeling.Hydrologic sciencesavi2101International Research Institute for Climate and SocietyArticlesAir-ground temperature coupling and subsurface propagation of annual temperature signalshttp://academiccommons.columbia.edu/catalog/ac:137644
Smerdon, Jason E.; Pollack, Henry N.; Cermak, Vladimir; Enz, John W.; Kresl, Milan; Safanda, Jan; Wehmiller, John F.http://hdl.handle.net/10022/AC:P:10992Wed, 24 Aug 2011 00:00:00 +0000Borehole-based reconstructions of ground surface temperature (GST) have been widely used as indicators of paleoclimate. These reconstructions assume that heat transport within the subsurface is conductive. Climatic interpretations of GST reconstructions also assume that GST is strongly coupled to surface air temperature (SAT) on timescales of decades and longer. We examine these two assumptions using records of SAT and subsurface temperature time series from Fargo, North Dakota; Prague, Czech Republic; Cape Henlopen State Park, Delaware; and Cape Hatteras National Seashore, North Carolina. The characteristics of downward propagating annual temperature signals at each site clearly indicate that heat transport can be described as one-dimensional conduction in a homogeneous medium. Extrapolations of subsurface observations to the ground surface yield estimates of annual GST signals and allow comparisons to annual SAT signals. All annual GST signals are modestly attenuated and negligibly phase shifted relative to SAT. The four sites collectively demonstrate that differences between annual GST and SAT signals arise in both summer and winter seasons, in amounts dependent on the climatic setting of each site.Atmospheric sciences, Paleoclimate science, Hydrologic sciencesjes2155Lamont-Doherty Earth ObservatoryArticlesSimulating heat transport of harmonic temperature signals in the Earth's shallow subsurface: Lower-boundary sensitivitieshttp://academiccommons.columbia.edu/catalog/ac:137635
Smerdon, Jason E.; Stieglitz, MarcWed, 24 Aug 2011 00:00:00 +0000We assess the sensitivity of a subsurface thermodynamic model to the depth of its lower-boundary condition. Analytic solutions to the one-dimensional thermal diffusion equation demonstrate that boundary conditions imposed at shallow depths (2-20 m) corrupt the amplitudes and phases of propagating temperature signals. The presented solutions are for: 1) a homogeneous infinite half-space driven by a harmonic surface-temperature boundary condition, and 2) a homogeneous slab with a harmonic surface-temperature boundary condition and zero-flux lower-boundary condition. Differences between the amplitudes and phases of the two solutions range from 0 to almost 100%, depending on depth, frequency and subsurface thermophysical properties. The implications of our results are straightforward: the corruption of subsurface temperatures can affect model assessments of soil microbial activity, vegetation changes, freeze-thaw cycles, and hydrologic dynamics. It is uncertain, however, whether the reported effects will have large enough impacts on land-atmosphere fluxes of water and energy to affect atmospheric simulations.Atmospheric sciences, Hydrologic sciences, Geophysicsjes2155Lamont-Doherty Earth ObservatoryArticlesConduction-dominated heat transport of the annual temperature signal in soilhttp://academiccommons.columbia.edu/catalog/ac:137654
Smerdon, Jason E.; Pollack, Henry N.; Enz, John W.; Lewis, Matthew J.Wed, 24 Aug 2011 00:00:00 +0000Conductive heat transport of temperature signals into the subsurface is a central assumption of ground surface temperature (GST) reconstructions derived from present-day temperatures in deep boreholes. Here we test this assumption and its implications for annual relationships between GST and surface air temperature (SAT) by analyzing two decades of shallow soil temperature (0.01-11.7 m) and SAT time series measured at Fargo, North Dakota. We spectrally decompose each of these temperature time series to determine the amplitude and phase of the annual signal at each depth. Conductive heat transport of a harmonic temperature signal in a homogeneous medium is characterized theoretically by exponential amplitude attenuation and linear phase shift with depth. We show that transport of the annual signal in the soil at Fargo follows these theoretical characterizations of conduction closely: the depth dependence of both the natural logarithm of the amplitude and the phase shift are highly linear. Interval wave velocities and thermal diffusivities calculated as functions of depth suggest a diffusivity gradient in the upper meter of the soil. We estimate the annual signal at the ground surface by extrapolating amplitude and phase shift regression lines upward to the surface. We compare this estimate of the annual signal at the ground surface to the annual signal contained in the SAT and show the ground surface signal to be attenuated ~20% and negligibly phase shifted relative to the SAT.Atmospheric sciences, Hydrologic sciencesjes2155Lamont-Doherty Earth ObservatoryArticlesVariable seasonal coupling between air and ground temperatures: A simple representation in terms of subsurface thermal diffusivityhttp://academiccommons.columbia.edu/catalog/ac:137641
Pollack, Henry N.; Smerdon, Jason E.; Keken, Peter E. vanhttp://hdl.handle.net/10022/AC:P:10991Wed, 24 Aug 2011 00:00:00 +0000The utility of subsurface temperatures as indicators of temperature changes at Earth's surface rests upon an assumption of strong coupling between surface air temperature (SAT) and ground surface temperature (GST). Here we describe a simple representation of this coupling in terms of a variable thermal diffusivity in the upper meter of the subsurface. The variability is tied to daily SAT, precipitation, and snow cover, but does not incorporate the physical details of these and the many other factors that influence the air-ground interface in many high-fidelity land-surface models. Our simple model reduces the difference between observed and modeled temperatures by a factor of 3 to 4 over a model with uniform diffusivity driven only by SAT. This simple representation of air-ground coupling offers a means of simulating subsurface temperatures using only archived meteorological records and creates the potential for examining the long term character of air-ground temperature coupling.Atmospheric sciences, Paleoclimate science, Hydrologic sciencesjes2155Lamont-Doherty Earth ObservatoryArticlesBorehole climate reconstructions: Spatial structure and hemispheric averageshttp://academiccommons.columbia.edu/catalog/ac:137647
Pollack, Henry N.; Smerdon, Jason E.Wed, 24 Aug 2011 00:00:00 +0000Ground surface temperature (GST) reconstructions determined from temperature profiles measured in terrestrial boreholes, when averaged over the Northern Hemisphere, estimate a surface warming of ~1 K during the interval AD 1500-2000. Other traditional proxy-based estimates suggest less warming during the same interval. Mann et al. [2003a] have raised two issues with regard to borehole-based reconstructions. The first focuses on the need for spatial gridding and area-weighting of the ensemble of borehole-based GST reconstructions to yield an average hemispheric reconstruction. The second asserts that application of optimal detection techniques show that the GST only weakly displays the spatial structure of the surface air temperature (SAT). We demonstrate the consistency of GST warming estimates by showing that over a wide range of grid element area and occupancy weighting schemes, the five-century GST change falls in the range of 0.89-1.05 K. We examine the subhemispheric spatial correlation of GST and SAT trends at various spatial scales. In the 5-degree grid employed for optimal detection, we find that the majority of grid element means are determined from three or fewer boreholes, a number that is insufficient to suppress site-specific noise via ensemble averaging. Significant spatial correlation between SAT and GST emerges in a 5-degree grid if low-occupancy grid elements are excluded, and also in a 30-degree grid in which grid element means are better determined through higher occupancy. Reconstructions assembled after excluding low-occupancy grid elements show a five-century GST change in the range of 1.02-1.06 K.Atmospheric sciences, Climate change, Hydrologic sciencesjes2155Lamont-Doherty Earth ObservatoryArticlesA model study of the effects of climatic precipitation changes on ground temperatureshttp://academiccommons.columbia.edu/catalog/ac:137661
Lin, Xiaohua; Smerdon, Jason E.; England, Anthony W.; Pollack, Henry N.http://hdl.handle.net/10022/AC:P:10996Wed, 24 Aug 2011 00:00:00 +0000Temperature changes at the Earth surface propagate into the subsurface and leave a thermal signature in the underlying soil and rock. Inversions of subsurface temperature measurements yield reconstructions of ground surface temperature (GST) histories that provide estimates of climatic changes. A question remaining in the interpretation of reconstructed GST histories is the extent to which GST changes reflect changes principally in surface air temperature (SAT), or whether other factors may be significant. Here we use a Land Surface Processes (LSP) model to examine the influence of precipitation changes on GST and subsurface temperature and moisture fields on annual to decadal timescales. We model soil and vegetation conditions representative of a prairie region in the southern Great Plains of North America and force the model with meteorological data synthesized from a typical year in the region. Model responses are observed after changes in the amount of daily precipitation, the intensity and frequency of daily precipitation, and the diurnal and seasonal timing of precipitation. We show that: (1) increasing daily precipitation cools mean annual GST, (2) increasing the intensity and reducing the frequency of daily precipitation, while holding the annual amount of precipitation constant, cools mean annual GST, and (3) shifting maximum precipitation to occur in the warmest months cools mean annual GST. We compare modeled results to observed precipitation changes during the 20th century and conclude that the observed precipitation changes would cause only small changes to GST within the modeled region, on the order of 0.1 K or less.Atmospheric sciences, Hydrologic sciencesjes2155Lamont-Doherty Earth ObservatoryArticlesCharacterizing land surface processes: A quantitative analysis using air-ground thermal orbitshttp://academiccommons.columbia.edu/catalog/ac:136968
Smerdon, Jason E.; Beltrami, Hugo; Creelman, Chance; Stevens, M. Brucehttp://hdl.handle.net/10022/AC:P:10873Wed, 10 Aug 2011 00:00:00 +0000A quantitative analysis of thermal orbits is developed and applied to modeled air and ground temperatures. Thermal orbits are phase-space representations of air and ground temperature relationships that are generated by plotting daily or monthly ground temperatures against air temperatures. Thermal orbits are useful descriptive tools that provide straightforward illustrations of air and ground temperature relationships in the presence of land surface processes related to snow cover, soil freezing, and vegetation effects. The utility of thermal orbits has been limited, however, by the lack of quantitative analyses that describe changes in orbits across different environments or in time. This shortcoming is overcome in the present study by developing a linear regression analysis of thermal orbits that allows changes to be tracked in time and space and as a function of depth within the subsurface. The theory that underlies the thermal orbit regression analysis is developed herein, and the utility of the application is demonstrated using controlled model experiments.Atmospheric sciences, Hydrologic sciencesjes2155Lamont-Doherty Earth ObservatoryArticlesEstimating the depth and shape of subglacial Lake Vostok's water cavity from aerogravity datahttp://academiccommons.columbia.edu/catalog/ac:135975
Studinger, Michael; Bell, Robin E.; Tikku, Anahita A.Wed, 20 Jul 2011 00:00:00 +0000We use aerogravity data to estimate the water depth of subglacial Lake Vostok in East Antarctica. The inversion produces the first bathymetry map covering the entire lake. Lake Vostok consists of two sub-basins separated by a ridge with very shallow water depths. The deeper southern sub-basin is approximately double the spatial area of the smaller northern sub-basin. The close correlation between the pattern of basal melting and freezing and the bathymetric structure has important ramifications for the water circulation and the sediment deposition. We estimate the lake volume to be 5400 ± 1600 km3.Hydrologic sciences, Marine geology, Geophysicsreb4Lamont-Doherty Earth ObservatoryArticlesTectonically controlled subglacial lakes on the flanks of the Gamburtsev Subglacial Mountains, East Antarcticahttp://academiccommons.columbia.edu/catalog/ac:135956
Bell, Robin E.; Studinger, Michael; Fahnestock, Mark A.; Shuman, Christopher A.Wed, 20 Jul 2011 00:00:00 +0000The morphology of surface lakes strongly influences their ecology and limnology (Wetzel, 2001). This morphology is a result of both the geologic processes that produce topographic basins and the regional climatic and local hydrologic processes that control water depth and sediment infilling (Carroll and Bohacs, 1999). Although basin forming processes range from glacial scour to meteorite impacts (Cohen, 2003), the deepest, oldest surface lakes are tectonically controlled (Meybeck, 1995) and contain diverse exotic ecosystems (Rossiterm and Kawanabe, 2000). Subglacial lakes are also thought to be ancient systems that may contain exotic biota (Bulat et al., 2004; Karl et al., 1999; Priscu et al., 1999). Here we present evidence for the scale and configuration of 2 large subglacial lakes in East Antarctica that together with Lake Vostok define a province of major lakes on the flanks of the Gamburtsev Subglacial Mountains. Spatially-defined in the new Moderate Resolution Imaging Spectroradiometer (MODIS) imagery of Antarctica (T. Scambos et al., A MODIS-based mosaic of Antarctica: MOA, submitted to Remote Sensing of Environment, 2005, hereinafter referred to as Scambos et al., submitted manuscript, 2005), these lakes are aligned parallel to Lake Vostok. Other data shows that they are distinguished by distinct gravity lows, flat ice surface slopes and have estimated water depths of at least 900 m. Surface elevation data indicates that large deep subglacial lakes have a profound influence on the regional ice sheet topography and probably ice sheet flow. These deep subglacial lakes with elongate, rectilinear morphology are tectonically controlled features. Unlike the shallow lakes in West Antarctica and beneath Dome Concordia, these deep subglacial lakes remained stable environments through many glacial cycles since their origin 10-35 Ma enabling the development of novel ecosystems.Hydrologic sciences, Geophysicsreb4Lamont-Doherty Earth ObservatoryArticlesSubglacial sediments: A regional geological template for ice flow in West Antarcticahttp://academiccommons.columbia.edu/catalog/ac:135979
Studinger, Michael; Bell, Robin E.; Blankenship, Donald D.; Finn, Carol A.; Arko, Robert A.; Morse, David L.; Joughin, Ianhttp://hdl.handle.net/10022/AC:P:10762Wed, 20 Jul 2011 00:00:00 +0000We use aerogeophysical data to estimate the distribution of marine subglacial sediments and faultâ€bounded sedimentary basins beneath the West Antarctic Ice Sheet (WAIS). We find that significant ice flow occurs exclusively in regions covered by subglacial sediments. The onsets and lateral margins of ice streams coincide with the limit of marine sediments. Lateral margins are also consistently linked with faultâ€bounded basins. We predict that the inland migration of ice streams B and C 1 towards the ice divide outside the region covered by marine or rift sediments is unlikely. The subglacial geology has the potential to modulate the dynamic evolution of the ice streams and the WAIS.Hydrologic sciences, Marine geology, Geophysicsreb4, raa10Lamont-Doherty Earth ObservatoryArticlesAnomalous accumulation rates in the Vostok ice-core resulting from ice flow over Lake Vostokhttp://academiccommons.columbia.edu/catalog/ac:135967
Leonard, Katherine; Bell, Robin E.; Studinger, Michael; Tremblay, Brunohttp://hdl.handle.net/10022/AC:P:10760Wed, 20 Jul 2011 00:00:00 +0000Hydrologic sciences, Physical oceanographyreb4, bt63Lamont-Doherty Earth ObservatoryArticles